Thursday, 4 June 2009 - 15.00
SISSA Lecture Room A
( CNR-INFM S3 - Modena )
"AB INITIO STUDY OF HYBRID INTERFACES FOR PHOTOVOLTAIC APPLICATIONS"
Metal-oxide semiconductors have been profitably investigated
for applications in catalytic systems and optoelectronic devices. In
particular, it has been largely demonstrated that the metal-oxide
nanoparticles may be sensitized to harvest visible radiation in working
solar cells, upon molecular dye functionalization. However, at present
the principles regulating interactions between the oxide layer and the
rest of the photovoltaic cell are poorly understood. Indeed, upon
molecular sensitization, the semiconductor surface interacts with
molecules in a wide range of possible scenarios, driving the formation
of hybrid interfaces with specific spatial arrangement and novel
electronic properties, and affecting both light harvesting and the
generation of the photovoltaic current.
In order to unravel these problems from a fundamental point of view, we
provide a microscopic description of oxide-based interfaces, by means of
first principles calculations, based on static and time-dependent
Density Functional Theory.
We focus on non-polar ZnO(10-10) surface in connection either with
natural organic dyes (anthocyanins) and with water solution. We first
characterize the optoelectronic properties of the dye both in the gas
phase in liquid water. Then, we consider the effects of water adsorption
on the ZnO surface, and the role of surface defects. Finally, the
adsorption of the molecular chromophore on the ZnO surface is presented.
Wednesday, 1 April 2009 - 16.00
SISSA Lecture Room A
( ICTP, Trieste )
"The fermi edge singularity, work statistics, and quantum quenches"
A quantum quench is a rapid change in time of a control parameter in the
hamiltonian describing a quantum, correlated many body system. The
physics of this paradigmatic nonequilibrium process, which has been
realized recently in the context of cold atoms, is of particular
interest in quantum critical systems. In this talk I will discuss a
fundamental way to characterize these processes using basic
thermodynamic variables and looking at their statistics. I will do so by
first elucidating the connection between a classic problem in condensed
matter physics, the Fermi edge singularity, the statistics of the work
done in a quantum quench, and quantum Jarzynski equalities. Using this
connection, I will then characterize the statistics of the work done on
a quantum Ising chain by quenching locally or globally the transverse
field, showing that for local quenches starting at criticality, the
probability distribution of the work displays an interesting edge
I will finally show that similar singularities emerge in other quantum
critical systems, such as the Dicke model..
Tuesday, 15 July 2008 - 15.00
SISSA Lecture Room D
Prof. Mike Gillan
( Department of Physics and Astronomy, University College London )
"First-principles statistical mechanics of thermal desorption"
Temperature programmed thermal desorption (TPD) is one
of the most widely used experimental methods for determining adsorption
energies of molecules on surfaces. To interpret such experiments, there
is a strong need for techniques for calculating thermal desorption rates
from first principles. I will present some of the methods and results
that we have we have obtained in the past two years at UCL.
Tuesday, 1 July 2008 - 16.00
SISSA Lecture Room A
( Dipartimento di Fisica and SOFT-INFM-CNR -Universita' di Roma "La
Sapienza", Rome, Italy )
"THE PRESENT UNDERSTANDING OF THE VIBRATIONAL DYNAMICS IN GLASSES"
After almost ten years of application of the Inelastic X-ray Scattering
(IXS) technique, which complements the well established Inelastic
Neutron Scattering (INS) one, the main characteristics of the high
frequency (THz) collective modes in topologically disordered systems
have been identified. Despite the contributions of this new experimental
tool, less is know about the collective excitations of glasses in a
momentum-energy region that lie between the IXS (Q>1 nm-1) and the
traditional Brillouin Light Scattering (Q<0.04 nm-1) domains. Very
recently, the first steps were taken to fill this gap using the
synchrotron based UV Brillouin spectroscopy.
In this talk I will review what is the present understanding on the high
frequency dynamics of glasses, as obtained by INS and IXS experiments.
Moreover I will briefly present new measurements of the sound
attenuation in vitreous silica, performed by UV Brillouin spectroscopy,
for Q values up to 0.12 nm-1. These data, partially bridging the gap
between the existing BLS and IXS data, allows us to depict a coherent
description of the sound attenuation phenomenon in v-SiO2, and to reveal
the existence of very long range stress correlations in this material.
Monday, 30 June 2008 - 16.00
SISSA Lecture Room A
( Dept. of Theoretical, Atomic and Optical Physics, Univ. of Valladolid, Spain )
"ON THE OVERALL SCALING OF THE KOHN-SHAM POTENTIAL AND THE VIRIAL AS A DENSITY FUNCTIONAL"
Consequences of uniform coordinate scaling of the independent particle
kinetic energy functional of density functional theory, Ts[n], are
discussed. A scaling relation for the functional derivative of Ts[n] is
obtained which leads to a scaling relation for the Kohn-Sham potential,
while the scaling of the Kohn-Sham equations also provides information
on the scaling of the eigenvalues. It is also proved that the scaling
relation for the functional derivative of Ts[n] can be obtained by
direct functional differentiation of the scaling expression for Ts[n].
Numerical evidence of such a scaling are discussed. An expression is
deduced for the virial in terms of the ground state density and the
corresponding Kohn-Sham potential. It is shown that the virial is the
kinetic energy functional for a 2-electron systems while for N-electron
systems the external potential as a functional of the density preclude
us from having an explicit form for the non-interacting kinetic energy
functional. An approximated kinetic energy functional for N-electron
systems, based on the virial, is presented and some numerical results
Monday, 30 July 2007 - 16.00
SISSA Lecture Room A
( Department of Physics,
Sharif University of Technology and UC Santa Cruz
Santa Cruz, CA 95064 USA)
"NEGATIVE DIFFERENTIAL RESISTANCE IN NANOCONTACTS AND ATOMIC CHAINS"
NDR has been observed in several devices, in particular resonant double
barrier structures. It occurs when with increasing bias the resonant state
moves in the gap of one of the contacts. In this talk, we present another
mechanism, which occurs in nanocontacts or atomic chains connecting two
contacts. It has to do with the localization of states at the two contacts
and a reduction in the local density of states (LDOS) of the right/left
leads. We express the conditions necessary for the observation of NDR, and
as an illustration, present our findings for atomic chains bridging two
capped carbon nanotubes or graphene ribbons.
Thuesday, 24 July 2007 - 10.00
SISSA Lecture Room A
MATTEO FARNESI CAMELLONE
( EMPA, Materials Science and Technology, Electronic/Metrology Laboratory,
CH-8600 Duebendorf, Switzerland)
"POINT DEFECTS IN CRYSTALLINE AND AMORPHOUS SILICA"
The essential limitations on gate insulator are related to the exponentially
increasing gate current as the thickness of the oxide is reduced, and the
effect of this current on both the functionality and reliability of devices
and circuits. Quantum mechanical (ab initio) calculations models can be used
to simulate the formation of atomic defects of a realistic material
structure. Density functional theory and Hartree Fock theory have been used
to model and study the nature of point defects in crystalline and amorphous
silica. The amorphous silica models have been generated using a combined
classical and ab inito molecular dynamics simulation scheme. The nature of
oxygen vacancies, the role of hydrogen species and self trapped holes in
SiO2 have been investigated.
Monday, 2 July 2007 - 16.00
SISSA Lecture Room A
( Texas A&M University, College Station, TX )
"COMPUTATIONAL STUDIES OF THE CATHODE REGION IN PROTON EXCHANGE FUEL CELLS"
Thursday, 28 June 2007 - 16.00
Aula A1 (3rd floor)
Dipartimento Scienze Chimiche
Università di Trieste, Edificio C11, Via Giorgeri 1
Prof. FRANCESCO GIANTURCO
( Università di Roma "La Sapienza" )
"Modelling radiation damage in biosystems mediated by slow electrons"
Wednesday, 13 June 2007 - 14.30
SISSA Lecture Room A
( Dipartimento di Fisica and ETSF, Università degli Studi di Milano )
"AB-INITIO STUDY OF THE BETA-TIN -> IMMA -> SH PHASE TRANSITIONS IN BULK
We present an ab-initio study of the lattice statics and dynamics of Si near the high-pressure Β-tin→Imma→
sh phase transitions.
In a first step, temperature effects are neglected and the phases are investigated with respect to their
stability. Herewith, the order of the phase transitions is determined and the results are compared with
In a second step, the temperature dependence of the transition pressure is investigated within the
quasiharmonic approximation. This yields a detailed study of the phonon frequencies of the structures
where especially the phonon frequencies at the point are inspected in detail. We found a soft-mode
behavior for the phase transition sh→Imma which can be used for the determination of the transition
pressure. A comparison of our data with the experimental ones shows that the phase transitions Β-
tin→Imma→sh have been already indicated in the Raman spectra even though not realized because of
The convergence of the phonon spectra is very important for the determination of the temperature
dependence of the transition pressure and a new method for accelerating the convergence has been
developed for that purpose. Furthermore, we have found a Kohn anomaly at the bct structure, however,
beyond the stability range of the Β-tin phase.
This work has been performed using the plane-wave pseudopotential approach to the density-functional
theory and the density-functional perturbation theory within the local density approximation as
implemented in the Quantum-Espresso package.
Thursday, 7 June 2007 - 15.00
SISSA Lecture Room A
( University of Virginia )
"SOLVATION OF IMPURITIES IN LIQUID HE DROPLETS:
A MIXED THEORETICAL/EXPERIMENTAL PERSPECTIVE"
Friday, 11 May 2007 - 10:00
( IBM Zurich )
"Metal-Carbon Nanotube Contacts: the Link between Structure and Electrical Behavior from First-Principles Calculations"
Field-Effect Transistors based on Carbon Nanotubes are promising
candidates for post-CMOS microelectronics. It has by now been
established that transport in these devices is dominated by the
Schottky barriers existing at the metal-channel interfaces. We used
Car-Parrinello molecular dynamics calculations to investigate the actual
structure of the metal-CNT interface for two representative metals,
Al and Pd. Our calculated Schottky-Barrier Heights (SBH) show a good
agreement with experiment. Moreover, we find a correlation between the
SBH and the nature of the chemical bonding at the interface.
Monday, 18 September 2006, 10.00 SISSA Room A
"WIGNER CRYSTALLIZATION IN LOW DIMENSIONAL AND POLARIZABLE SYSTEMS"
Among several possible microscopic scenarios for the metal-insulator
transition, Wigner crystallization involves uniquely the long-range Coulomb
repulsion betweenelectrons at low density. A considerable amount of recent
experiments have been accumulated in low dimensional (or anisotropic)
compounds, where the charge ordering phenomena observed at low temperatures
are either interpreted as some form of Wigner crystallization or ascribed to
the presence of long range Coulomb interactions. Motivated by these
observations, a model that describes Wigner crystallization in an
anisotropic environment will be presented in the first part of the seminar.
I will show that restricting the electron motion into layers or chains,
while keeping the full three-dimensional nature of the Coulomb interactions,
can result in a sizeable stabilization of the crystallized phase as compared
to the usual three or two-dimensional case. A sequence of structural
transitions of the electron crystal is also predicted upon varying the
density.In the second part, I will discuss the effect of electron-phonon
interaction on Wigner crystallization. In real solids the phonon dynamics
can be coupled to the electrons and in principle it cannot be neglected.
When electron-phonon interaction is strong, polarons are formed leading to
qualitative modification of the phase diagram.
Wednesday, 27 September 2006, 11.00 SISSA Room A
(Department of Physics, University of Alberta)
"PHASES OF HARD CORE BOSONS IN OPTICAL LATTICES"
Impressive scientific and technological advances in
trapping cold atoms in
optical lattices (OL) render it now feasible to create in
remarkably close experimental realizations of model
many-body systems long
thought of as of mostly academic interest. The possibility
the interactions, as well as of carrying out a direct
verification of quantitative predictions, has prompted
renewed effort in the
theoretical study of "exotic" phase of matters that one may
observe in OLs.
In this talk, we shall discuss two examples of many-body
display intriguing phase diagrams, both involving hard core
two-dimensional lattices; one is a single-component system
on a triangular
lattice, the other an isotopic mixture on the square
lattice. Results of
recent studies based on numerical (Quantum Monte Carlo)
simulations will be
Monday, 3 July 2006, 10.00 Lecture Hall A
ICTP Adriatico Guest House (lower level 1)
RICHARD M. MARTIN
(Dept. of Physics, University of Illinois
LSI Lab, Ecole Polytechnique)
"INSULATORS, METALS, AND FRACTIONALIZED STATES - THE MOTT TRANSITION AND THE LUTTINGER THEOREM"
Recent work has led to a new approach for understanding different states of
condensed matter: insulators, metals, and states with fractional quantum
numbers. The fundamental distinction for metals vs. insulators proposed by
Kohn in 1964 is the sensitivity to boundary conditions. This has been
extended in two ways: A theory of the insulating state  that provides a
quantitative measure applying to all systems independent of interactions.
Recent work  that generalizes the ideas to the topological behavior of
the wavefunction as a function of boundary conditi This approach
reveals the relation of fundamental concepts including the Aharonov-Bohm
effect, Luttinger theorem, fractional quantum Hall effect, and other
fractionalized states. This talk will give an overview of the ideas and will
focus upon the nature of the insulating state, the Luttinger theorem on the
volume enclose by the Fermi surface, and new proposals for the nature of a
- I.Souza, T. J. Wilkens, and R. M. Martin, "Polarization and localization
in insulators: generating function approach", PRB 62, 1666 2000).
- See, for example, Oshikawa, "Insulator, Conductor, and Commensurability:
A Topological Approach" PRL 90, 236401 (2003).
- A. Seidel, et al. "Incompressible Quantum Liquids and New Conservation
Laws", PRL 95, 266405 (2006).
Thursday, 29 June 2006, 11.00 SISSA Room B
(ILL, Grenoble, France)
"INVESTIGATION OF THE MOTTNESS IN THE TWO DIMENSIONAL HUBBARD MODEL USING CELLULAR DYNAMICAL MEAN FIELD THEORY"
I present a study of the 2-D Hubbard model (relevant for H-Tc
superconducting materials) close to the density-driven Mott metal-insulator
transition, using a Cluster-extension of Dynamical Mean Field Theory (the
CDMFT). In recent years, Dynamical Mean Field Theory (DMFT) has proved a
successful tool to access the physics of strongly correlated electron
systems. DMFT is a self-consistent mean-field approach which fully describes
the quantum-dynamics on a single site, neglecting by construction spatial
correlations. We show however that this is a too crude approximation in
describing systems where spatial correlations are fundamental, like for
example cuprate superconductor materials. Contrari to DMFT, CDMFT is able to
take into consideration the short ranged physics by replacing a single site
by a cluster or neighboring sites. We apply CDMFT to the 2-D Hubbard model,
studying its anomalous normal-state properties and the anomalous
superconductive state deriving from them.
Wednesday, March 29, 2006, 12:00 SISSA Room A
(Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca)
"Ab-initio study of oxygen vacancies in yttria-stabilized zirconia"
Zirconia (ZrO2) stabilized in the cubic fluorite phase by the addition of
yttria (Y2O3) is a fast oxygen conductor widely used in solid oxide fuel
cells and oxygen sensors. Although the number of carriers (oxygen vacancies)
increases with yttria content, the conductivity reaches a maximum for a
dopant concentration of 9 mol%, decreasing beyond this value. This complex
behaviour is believed to stem from interactions among defects, including the
formation of a complex of two vacancies aligned along á111ñ directions.
However, a compelling experimental evidence of this defect, which has also
been tentatively associated to prominent signals in EPR and optical spectra
of reduced samples, is still lacking. In fact, other extrinsic defects (such
as Ti) have also been claimed responsible for the spectroscopic signals. In
this work we have studied the electronic properties of paramagnetic
di-vacancy complexes by computing the EPR g-tensor from density functional
perturbation theory . The paramagnetic defects are modeled in periodic
supercells of zirconia with 10 or 14 mol% yttria containing up to 93 atoms.
The calculated EPR g-tensors of both a Zr3+ or a Ti3+ ion at the center of a
di-vacancy aligned along the á111ñ directions are compatible with the
experimental EPR signal. However, comparison of experimental optical
absorption spectra with calculated optical excitations at the B3LYP level
allows us to decide in favor of the Ti3+ di-vacancy complex . Preliminary
results will be also presented on the diffusion processes of oxygen
vacancies. The results show that the activation barrier for the diffusion of
a single vacancy does not depend only on the vacancy-yttrium interaction as
customarily assumed, but also on the position of the other vacancies, which
might also promote concerted multiple jumps.
- C. J. Pickard and F. Mauri, Phys. Rev. Lett. 88, 86403 (2002).
- F. Pietrucci, M. Bernasconi, C. Di Valentin, F. Mauri, and C. J. Pickard, Phys. Rev. B, in press.
Friday, 20 January 2006 - 16:00
SISSA Room A
( Cambridge University Centre for Computational Chemistry Department of Chemistry, University of Cambridge, UK )
"AB INITIO MOLECULAR DYNAMICS SIMULATIONS OF REDOX REACTIONS: THE MARCUS PERSPECTIVE"
Electron transfer reactions are among the most fundamental chemical processes and are crucial in a number of important biological processes, such as photosynthesis and cell respiration. Nature and chemists alike have been tuning electron donor (D) and acceptor (A) sites or their environments to obtain ET rates and relative D-A stabilities optimized for a particular task. Here we employ an atomistic theoretical approach based on molecular mechanics and ab initio molecular mechanics to quantitative predicts the effects of such modifications on parameters that control the ET within the Marcus theory perspective. In particular examples of ruthenium-amine complexes and quinones in different solvents will be discussed. Our work confirms recent experiments and helps to rationalize the differences in redox potentials and reorganization energies due to chemical substitutions and changes in the environments.
Thursday, 22 December 2005 - 11:00
SISSA room A
( Dept. of Physics, Chalmers University of Technology, Goteborg )
"IMPURITIES IN LOW-DIMENSIONAL ANTIFERROMAGNETS"
We present Monte Carlo results for the local magnetic response around vacancies in the 2D Heisenberg
model and we outline their relevance to NMR and susceptibility experiment (Cond-Mat/0511001). We also
discuss an effective potential between static vacancies and the relation of this quantity to the the
local VB order of quantum AF(Cond-mat/0512001).
Monday, 26 October 2005 - 11:00
SISSA room A
( Cornell University )
"OPTIMIZATION OF MANY-BODY WAVE FUNCTIONS AND TIME-EVOLUTION OPERATORS WITH AND WITHOUT THE FIXED-NODE BOUNDARY CONDITIONS"
I will (perhaps foolishly) try to discuss two disjoint topics in quantum Monte Carlo.
First, I will discuss some recent progress on the optimization of wave functions and
point out that different issues arise in optimizing the Jastrow and the determinantal parameters.
In the case of the Jastrow parameters, it is possible to gain a few orders of magnitude in
efficiency by adding terms to the straightforward expression for the Hessian of the energy that
are zero when the integrals are performed exactly, but that cancel much of the statistical fluctuations
for a finite Monte Carlo sample. I will also show the example of a very simple molecule for which we have learned
by optimizing a multideterminantal wave function that
- the fixed-node error of a single-determinant wave function is shockingly large and
- that it is very important to reoptimize the coefficients multiplying the determinants that one gets from a MCSCF calculation.
In the second part of the talk I will use the toy example of a simple harmonic oscillator in 1-dimension to demonstrate
- the differences in the EXACT propagator with fixed-node boundary conditions and the EXACT propagator without fixed-node boundary conditions
- a better approximation to the fixed-node propagator than the one usually employed
- a "cross-node" propagator that is a good approximation to the propagator without boundary conditions
- present some speculative ideas on combining this cross-node propagator with Sandro Sorella's stochastic reconfiguration idea to improve upon Ceperley's release-node algorithm.
Acknowledgements: much of the first part of this talk was done in collaboration with Claudia Filippi and has been recently published with her and are closely related to work done independently by Sandro Sorella. The ideas for the 2nd part of the talk were developed in the 1990's with the help of Andreas Savin, but have not yet been published.
Monday, 29 August 2005 - 16:00
SISSA room A
( Dipartimento di Ingegneria Meccanica, Politecnico di Bari, Bari, Italy )
"ADHESION AND FRICTION OF RUBBER"
The mechanical response of a compliant solid is of fundamental importance in a large number of industrial and hi-tech applications. Some examples are the structural adhesives used in the aerospace and automotive industries, the adhesive interlayer of laminated glasses, the thin films used as protective coatings in orthopedic implants, or a new class of adhesives which replicate the attachment systems of some biological species, e.g. the Gekko Gecko. In all such applications, the rheological properties of the layer, its thickness, the interfacial energy and the roughness of the substrate play a major role in controlling the "adhesive strength" of the joint. Adhesion is also fundamental in sliding friction on flat and rough surfaces and significantly affects the handling and breaking performances, e.g., of F1-tires. The interplay between adhesion and roughness is fundamental in all such applications. In fact, surface roughness can remove the adherence force almost completely: When an elastic body is brought into contact with a rigid rough substrate, a certain amount of elastic energy is stored at the interface, this elastic energy can be used to break the adhesive bonds, so that even a relative small surface roughness can completely remove the adhesion. In this talk it is shown how adhesion may be related to friction of rubber. We show that the sliding process may be considered as resulting from a closing crack at the front edge, and a opening crack at the trailing edge of the contact regions, and that, because of adhesion hysteresis, the amount of energy required to open the crack largely overcome the amount of energy recovered during crack closing, thus producing a net friction force. We also show that adhesion largely affect the area of real contact on rough surfaces even when the adherence force is completely removed, and explain why in many biological systems, showing a high adhesive ability, as for example the gecko foot pad, a very thin leaf-like plate (spatula) is found at the end of each thin fiber: The plate can easily bend to follow the long-wave surface roughness profile and therefore enhance adhesion.
Thursday, 26 May 2005 - 16:00
SISSA room B
( Molecular Biology Department Max Planck Institute for Biophysical Chemistry )
"New insights into the Metallobiology of Parkinson\u2019s disease: Structural and biological implications of Cu(II) binding to a-Synuclein"
The objective of our studies is to establish the role of metal ions in synucleinopathies at the molecular resolution currently available for other amyloidoses. In this work, the interaction of Cu(II) with a-Synuclein (AS) was studied under physiologically relevant conditions using a battery of low and high-resolution spectroscopic techniques (CD, EPR and NMR) and chemical modification.1 Cu(II) levels in the micromolar range were effective in accelerating AS aggregation. The interactions of Cu(II) and AS were characterized at single-residue resolution by NMR. We showed for the first time that Cu(II) binds to a long-range preformed interface located in the N-terminal domain of AS (KD=100nM). A second binding motif is located at the C-terminus, were Cu(II) binds with lower affinity (KD=50mM). Cu(II) as an structural probe indicated that AS adopts in solution an ensemble of conformations characterized by a well-defined long-range topology in the N-terminal domain and isolation of the NAC region from the surrounding environment. Cu(II) might act as a conformational switch, releasing long-range interactions that are critical to stabilize a soluble native auto-inhibited conformation of AS.2,3 The new insights into the structural basis of copper interaction with AS support a tighter link with other amyloid-related disorders such as Alzheimer\u2019s disease and prion disease, indicating that perturbations in copper metabolism may constitute a more widespread element in neurodegenerative disorders than recognized previously.
- Rasia et al, , Proc. Natl. Acad. Sci. U.S.A. (2005) 102, 2490.
- Fernandez et al, EMBO J. (2004) 23, 2039.
- Bertoncini et al, Proc. Natl. Acad. Sci. U.S.A. (2005) 102, 1430.
Tuesday, 17 May 2005 - 15:00 SISSA Room A
( INFM-DEMOCRITOS & Dipartimento di Fisica Teorica, Univ. Trieste )
"ORBITAL MAGNETIZATION AS A BULK PROPERTY OF EXTENDED SYSTEMS"
(Work performed in collaboration with D. Ceresoli, T. Thonhauser, and D. Vanderbilt)
The magnetic dipole moment of any finite sample is well defined, while it
becomes ill defined in the thermodynamic limit, due to the unboundedness of
the position operator. Effects due to surface currents and to bulk
magnetization are not easily disentangled. The corresponding electrical
problem, where surface charges and bulk polarization appear as entangled,
has been solved in the 1990s by the modern theory of polarization, based on
a Berry phase. We proceed here on a similar path, and we derive a bulk
expression for the orbital magnetization of a non-interacting (band)
insulator with broken time-reversal symmetry.
Our theory is limited to the case of vanishing (or commensurate) magnetic
field and zero Chern number. We start expressing magnetization in terms of
localized orbitals: the dissipationless current circulating in the sample is
decomposed in two contributions: the first arises from the internal
circulation of bulk-like Wannier functions in the interior of the sample,
while the second arises from net currents carried by the localized orbitals
at the boundary of the sample. While the fist term has an exact electrical
analogue, the second one is qualitatively new. We show that when both
contributions are included, the result can be transformed into the
Brillouin-zone integral of an elegant k-space expression, somehow
reminiscent of the Berry connection and curvature appearing in electrical
polarization and Hall conductivity. Our result is consistent with a recent
semiclassical argument by Niu and coworkers (cond-mat/0502340).
Numerical implementations on a 2d tight-binding model are used to illustrate
how circulating currents flow through the sample and to demonstrate the
correctness of the derived formula.
Interestingly, our final expression remains well-defined even for metals,
but it is not yet clear whether it is correct in that case. It is also
unclear whether it can be extended to insulators with nonzero Chern numbers.
Tuesday, 22 March 2005 11:00 SISSA Room A
(Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA)
"Accurate ab initio intermolecular potentials with a focus on flexible water"
Understanding the weak van der Waals forces which act
between molecules is essential for predicting the
spectroscopy of clusters and the properties of molecular
condensed phases. In the first half of the talk, I will
briefly review the ab initio theory of intermolecular
forces, in particular the symmetry-adapted perturbation
theory (SAPT), followed by a discussion of intermolecular
potentials and the approximations made in developing such
potentials (e.g., level of theory, finite basis sets, and
assumption of monomer rigidity). The second half of the
talk will be devoted to describing the development of an
accurate flexible potential for water explicitly dependent
on the monomer geometries. Why does no such purely ab
initio potential yet exist for this important and
ubiquitous substance? The answer is dimensionality:
developing a flexible water potential requires the sampling
of a 12-dimensional configuration space, while for rigid
water that space is only 6-dimensional. Since the accurate
calculation of interaction energy at each configuration
(grid point)is expensive, only recently have computational
resources become available to allow us to generate the
large number of points needed for an accurate
12-dimensional fit. The procedure used in selecting monomer
and dimer configurations will be described. The final fit
was performed to 240,000 grid points as well as to ab
initio flexible multipole moments and van der Waals
induction and dispersion coefficients. The fit will be
analyzed and its preliminary predictions will be discussed.
Tuesday, 22 February 2005, 14.00 SISSA Room A
(INFM-DEMOCRITOS, INFM-SLACS, and Dipartimento di Fisica Università di Cagliari)
"The atomic scale origin of crack resistance in brittle fracture"
We investigate the physical meaning of the intrinsic crack resistance in the
Griffith theory of brittle fracture by means of atomic-scale simulations. By
taking cubic SiC as a typical brittle material, we show that the widely
accepted identification of intrinsic crack resistance with the free surface
energy underestimates the energy release rate. Strain dependence of the
Young's modulus and surface energy, as well as allowance for lattice
trapping, improve the estimate of the crack resistance. In the smallest
scale limit, crack resistance can be fitted by an empirical elasto-plastic model.
- A. Mattoni, L. Colombo, and F. Cleri, Phys. Rev. B70, 094108 (2004)
- A. Mattoni, L. Colombo, and F. Cleri, submitted for publication (Jan. 2005)
Thursday, 10 February 2005, 16.30 SISSA Room D
Anna Maria Capelli
(GlaxoSmithKline S.p.A., (Verona))
Computational aspects of rational Drug Design in GSK
Tuesday, 1 February 2005, 16.00 SISSA Room B
Rodolfo Del Sole
(INFM and Dipartimento di Fisica, Università di Roma "Tor Vergata")
"Ab-initio theory of excited states: electronic and optical properties of surfaces"
The microscopic study of complex systems has nowadays
reached a high level of accuracy that allows for a deep
understanding of the electronic excitations.
Ab-initio descriptions of experiments such as direct or
inverse photoemission, optical absorption, electron energy
loss, have become possible thanks to the huge progress in
theory and the increased computational power.
Charged excitations, as well as neutral excitations, can
now be studied within the Many-Body Perturbation Theory
based on the Green's function formalism.
Optical spectra can be calculated with inclusion of the
electron hole interaction by solving the Bethe Salpeter
equation (BSE) within the framework of Green's function
theory. Moreover, optical spectra can be nowadays also well
described within the Time Dependent Density Functional
In this seminar we will present examples of calculations of
surface optical properties according to different
approximations. In particular, we will show that the BSE
and TDDFT approaches yield the same optical spectrum for
Tuesday, 7 December 2004, 11.00 Seminar Room ICTP M. B. (first floor)
(Elettra Synchrotron Light Laboratory, Trieste)
"Collective dynamics in disordered systems studied by inelastic UV scattering"
The recent construction of an Inelastic UltraViolet
Scattering (IUVS) beamline at the ELETTRA Synchrotron Light
Laboratory opens new possibilities for studying the density
fluctuation spectrum, S(Q,E), of disordered systems in the
mesoscopic momentum (Q) and energy (E) transfer region not
accessible by other spectroscopic techniques. We will
present first IUVS results obtained on two prototype
samples such as liquid water and fused silica [1,2]. In
water we were able to measure the temperature dependence of
the structural relaxation time showing that the divergence
in the transport properties does not need an underlying
critical behavior but can be explained in the framework of
the Mode Coupling Theory . In vitreous silica IUVS
experiments gave clear experimental evidence of the
presence of a step in the sound attenuation coefficient at
wavelengths between 6 and 60 nm thus locating a
characteristic length where sound waves interfere with
- C. Masciovecchio, S.C. Santucci, A. Gessini, S. Di
Fonzo, G. Ruocco, and F. Sette, Physical Review Letters
92, 255507, (2004)
- C. Masciovecchio, A. Gessini, S. Di Fonzo, L. Comez,
S.C. Santucci and D. Fioretto, Physical Review Letters 92,
- F. Sciortino, P. Gallo, P. Tartaglia, S. H. Chen,
Physical Review E 54, 6331, (1996). F.W. Starr, M.-C.
Bellissent- Funel, H. E. Stanley, Physical Review Letters
82, 3629, (1999). F.W. Starr, F. Sciortino, H. E. Stanley,
Physical Review E 60, 6757, (1999).
Monday, 29 November 2004, Università di Trieste, Aula Informatica del Dipartimento di Scienze Chimiche, Edificio C11, via Giorgieri 1
(Department of Chemistry, University of Oslo)
"THE APPLICATION OF DENSITY-FUNCTIONAL RESPONSE THEORY TOLARGE MOLECULAR SYSTEMS"
With recent advances in computational techniques, it has
become possibile to apply response theory to the
calculation of properties of molecular systems larger than
that of previous systems. In the present talk, some of
these advances are reviewed, with emphasis on properites
such asexcitation energies, polarizabilities, and indirect
nuclear spin--spincoupling constants calculated using
Thursday, 14 October 2004, 16.30 SISSA Room B
"Induced Fit and Entropy of Structural Adaptation in the Formation of Protein DNA Complexes"
Tuesday, 14 September 2004, 17.30 SISSA Room A
(Lab. of Computational Chemistry and Biochemistry - EPFL Lausanne)
"Electron Transfer Description via charge restrain QM/MM dynamics"
We introduce a new quantum mechanics/ molecular mechanics
based method to drive electron transfer reactions. Our
approach uses the dynamically restrained electrostatic
potential derived charges of the quantum atoms as a
reaction coordinate and allows an estimation of the free
energy barrier of the electron
transfer process. Moreover, it provides an accurate
description of the electronic structure changes and of the
nuclear reorganization associated with the reaction. We use
the method to describe the electron-transfer induced
dissociation of the m-chloro-cyano-benzene radical anion in
The reaction is triggered by solvent reorganization by a
change in the coordination water shell around the cyano
nitrogen atom. At the onset of the reaction, charge-spin
segregation is observed. The negative charge is transferred
to the leaving Cl, while the spin density localizes on the
non-saturated carbon atom of the benzene ring. The
calculated free energy barrier of dissociation is in good
quantitative agreement with the experimental data.
This type of study can be extended to the ET description in
biological systems, and can find practical applications in
cases in which a charge transfer is connected to a complex
geometric reaction coordinate and therefore traditional
thermodynamic integration is difficult to apply.
Tuesday, 14 September 2004, 10.00 SISSA Room A
(Nanochemistry Research Institute, Curtin University of Technology)
"Molecular mechanism of caspase activity regulation"
Cysteine-dependent aspartic proteases (caspases) are a
family of enzymes, which play a crucial role in programmed
cell suicide . This is a key cellular process for
multicellular organisms. Indeed irregular apoptosis is
associated with diseases such as cancer or Alzheimer.
Caspases are dimeric
proteins that accumulate in all eukaryotic cells in the
form of low-activity proenzyme precursors. Proteolytic
cleavage of specific sites triggers conformational changes
that lead to full activation, and thus to the initiation of
the apoptotic cascade. We have used a number of different
computational techniques, from QM/MM to classical MD to
structure-based thermodynamic analysis methods, in order
to investigate the molecular mechanisms that regulate
caspase and procaspase activity. These studies allowed the
characterisation of the chemical steps of the enzymatic
mechanism and of the structural rearrangements on the
pathway leading to a procaspase activation. They also
enabled the identification of the most important residues
for folding and dimerization in all the caspases and
procaspases. Finally, the folding pathways of different
classes of procaspases were also studied . A coherent
picture emerges indicating that the activation of
procaspases is triggered by the formation of a small
number of interactions at the dimer interface that
stabilize the active site loops in the active conformation.
- Earnshaw, W. C., Martins, L. M., and Kaufmann, S. H. Annu.Rev Biochem, 1999, 68, 383-424.
- M.Sulpizi, A. Laio, J. VandeVondele, A. Cattaneo, U. Rothlisberger, P.Carloni. Proteins, 2003, 52, 212-224.
- Piana, S. and Rothlisberger, U. Proteins, 2004, In Press
- Piana, S., Sulpizi, M., and Rothlisberger, U. Biochemistry, 2003, 42, 8720-8728.
- Piana, S., Taylor, Z., and Rothlisberger, U. Manuscript, Submitted.
Wednesday, 25 August 2004, 11.00 SISSA Room A
Renata M. M. Wentzcovitch
(Dept. of Chemical Engineering and Materials Science, Minnesota Supercomputer Institute for Digital Technology and Advanced Computations University of Minnesota, Minneapolis)
"Phase transition in MgSiO3 perovskite in the earth's lower mantle"
A new polymorph of MgSiO3 with the CaIrO3 structure and
more stable than the Pbnm-perovskite phase has been
identified by first-principles computations.
High-temperature calculations within the quasiharmonic
approximation indicate that this phase transition occurs at
pressure-temperature ( P-T) conditions expected in the
vicinity of the D" discontinuity. The D" region, i.e., the
bottom 250 km of the mantle, is know for its abnormal
properties attributed to the formation of a thermochemical
boundary layer existent between two dissimilar regions,
core and mantle, that don't mix today. Therefore, this
phase transition provides a new paradigm for interpreting
abnormal seismic properties of D". We have followed up with
calculations of its thermoelastic properties and attempt to
address some of these abnormal properties in light of this
Monday, 30 August 2004, 11.00 SISSA Room A
(Department of Physics, Yarmouk University (Irbid- Jordan))
"Exact-exchange Kohn-Sham density functional theory calculations of the electronic Structure semiconductors"
The exact-exchange (EXX) Kohn-Sham density functional
theory approach will be described and used to calculate the
electronic structures of the zincblende phase of AlN, GaN
and InN. In these calculations the Ga 3d and In 4d
electrons are treated for the first time, within EXX, as
valence states. For comparison with previous calculations
they are also treated and as part of the frozen core. Our
EXX results for AlN and GaN (obtained with the semicore Ga
3d electrons included as core states) are found to be in
excellent agreement with the similarly calculated values
and the available experimental data. When the semicore d
electrons are treated as valence states, the EXX bandgap of
ZB-GaN is found to be in excellent agreement with the GW
results, and the results of the two methods are
significantly smaller than experiment. For InN, where the
application of the GW approach is problematic, due the
negative LDA bandgap, the EXX approach allows a fully
consistent treatment. Contrary to the common believe, the
removal of the self-interaction, provided by the EXX
approach, does not account for the large discrepancies
between the LDA (or GGA) results for the position of the
semicore d bands and experiment. The prospects of
overcoming the difficulties encountered by relaxing the
semicore d electrons by performing GW calculations based on
EXX results will be discussed.
Friday, 20 August 2004, 11.00 SISSA Room A
(Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur, Bangalore, INDIA)
"Structural and Vibrational Consequences of Reduced Coordination"
Tuesday, 27 July 2004, 13.00 SISSA Room A
(University of Trieste, Department of Chemistry)
"Anticancer Ruthenium Complexes"
In recent years several ruthenium compounds were found to
have very promising anticancer activity, frequently
different from that of Pt drugs, in animal tumor modelsand
in preclinical trials. Two ruthenium compounds developed in
Europe have nowbeen introduced into clinical trials: the
first was NAMI-A, [imH][trans-RuCl4(dmso-S)(im)] (im =
imidazole, Figure), a non-cytotoxic Ru(III)-dmso compound
developed inTrieste, that proved to have excellent activity
against disseminated solid tumors (metastases). NAMI-A has
accomplished phase I clinical trials and will hopefully
enter phase II soon. The second compound that reached phase
I trials at the end of 2003 is [indH][trans-RuCl4(ind)2]
(ind = indazole). This complex, developed by Bernhard
Keppler and termed KP1019, proved to be active against
platinum-resistant colorectal tumors.The lecture will be
focused on NAMI-A along the following topics: chemical
behavior of NAMI-A in physiological solution and in the
presence of biological reducing agents; anticancer
activity; mechanistic hypotheses; future developments.For
recent review on NAMI-A see refs 1 and 2.
- E. Alessio, G. Mestroni, A. Bergamo, G. Sava in "Metal
Ions and Their Complexes in Medication and in Cancer
Diagnosis and Therapy", Vol. 42 of Met. Ions Biol. Syst.,
A. Sigel and H.Sigel, eds., M. Dekker: New York, 2004, pp.
- E. Alessio, G. Mestroni, A. Bergamo, G. Sava, Curr.
Topics Med. Chem., in press.
Monday, 26 July 2004, 11.00 SISSA Room A
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague
"True stabilization energies for H-bonded and stacked structures of DNA base pairs and aminoacids pairs: complete basis set calculations at the MP2 and CCSD(T) levels"
Stabilization energies of H-bonded and stacked structures
of DNA base pairs and aminoacids pairs were determined in
the gas-phase optimized as well as crystal structures.
Stabilization energies were determined as the sum of the
complete basis set limit of MP2 stabilization energies and
CCSD(T) correction term. Final stabilization energies are
very substantional, much larger than published previuously
what is especially true for stacked structures. On the
basis of compariosn with experimental data it is conlcluded
that the present values represent the lower boundary of the
true stabilization energies.
The surprising stabilization of stacked structures can
significantly change the present view on the origin of
stabilization of DNA and proteins.
Friday, 9 July 2004, 11.00 SISSA Room A
Carlos G. LEVI
(Materials Dept., University of California, Santa Barbara)
"FUNDAMENTAL ISSUES IN THERMAL BARRIER SYSTEMS FOR ADVANCED GAS TURBINES"
Thermal barrier coatings (TBCs) are applied to actively
cooled gas turbine components to reduce the operating
temperature of the structural superalloy, thus
increasing its life, and/or to enable substantial
increments in the gas temperature and thus the efficiency
of the engine without compromising the durability of
the component. The coating system is multi-layer and
multifunctional, comprising a refractory oxide "top coat"
(10-250 µm) which provides thermal insulation, a
thin (~5 µm) "thermally grown (aluminum) oxide" (TGO)
interlayer that imparts oxidation resistance, and an
underlying metallic bond coat (50-100 µm) whichs upplies Al
to sustain the formation of the TGO. The established
systems are typically ZrO2+7ħ1%YO1.5 (7YSZ) on single-phase
(Ni,Pt)Al or two-phase (Ni,Co)CrAlY
TBCs are arguably the single most important materials issue
in enabling new advances in gas turbine technology,
comparable in impact to the combined developments
in superalloy design and cooling engineering over the past
30 years. However, current systems are not exploited up to
their maximum potential because of concerns
about their reliability. It is also evident that the
demands of new engine designs will exceed their performance
capabilities. A host of alternate materials has
emerged, primarily aimed at reducing the thermal
conductivity and/or improving the morphological stability
of the top coat. In general, these materials fall into
two groups, one based on co-doping of YSZ with one or more
rare earth oxides, and the other on replacing YSZ with a
rare earth zirconate, which may also be
co-doped. Implementation of these materials, however, is
hindered by a paucity of fundamental understanding of
several issues. For example, there is inadequate
understanding of the role of chemical composition on
thermal transport through the top coat, on the evolution
and/or stability of the microstructure vis-à-vis
phase constitution and morphology, as well as on the
mechanical properties of the oxide and related failure
mechanisms. The TGO, which is the major source of
strain incompatibility within the system, often develops
undulations of increasing amplitude with thermal cycling
which result from a combination of in-plane
growth stresses, cyclic plasticity and phase
transformations in the underlying bond coat. These
undulations are a source of interfacial separations that
eventually lead to spallation of the insulating layer.
Regarding the bond coat, the major issues result from
interdiffusion with the substrate and the need for
adequate diffusion barriers. Interdiffusion results not
only in changes in the phase constitution and mechanical
properties of both bond coat and substrate, but
also on the migration of deleterious impurities, e.g. S, to
the metal/oxide interface with attendant loss of adherence.
This presentation will discuss the general aspects of the
problem and the issues needing further understanding,
especially from the modeling arena, drawing on
current research activities at UCSB and partner
institutions. (Research sponsored by the Office of Naval
Research and an international collaborative research
program sponsored by the National Science Foundation and
the European Commission.)
Tuesday, 6 July 2004, 11.00 SISSA Room A
Rainer D. BECK
(Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland)
"Quantum State Resolved Studies of Gas/Surface Reaction Dynamics"
Laser light is a powerful tool for detailed experimental
studies of chemical reactions at the gas/surface interface.
It can be used to prepare molecules incident on a solid
surface in specific quantum states for state resolved
reactivity measurements (1). We have used this technique to
measure state resolved reaction cross sections for the
dissociative chemisorption of methane (CH4 results provide
a comparison of the efficacy of energizing different
degrees of freedom of the incident molecule for crossing
the reaction barrier (2). Different cross sections for
nearly isoenergetic vibrational states clearly demonstrates
the presence of mode specificity in this gas - surface
reaction. For CD2H2, we observed up to a factor of 5
greater reaction probability with two quanta of excitation
in one C-H bond versus one quanta in each of two C-H bonds
(3) . These results clearly exclude the possibility of
statistical models correctly describing the mechanism of
this process and emphasize the importance of
full-dimensional calculations of the reaction dynamics.
- M.P. Schmid, P. Maroni, R.D. Beck and T.R. Rizzo, Rev. Sci. Inst., 74, 4110 (2003)
- M.P. Schmid, P. Maroni, R.D. Beck and T.R. Rizzo, J. Chem. Phys. 117, 8603 (2002)
- R.D. Beck, P. Maroni, D. C. Papageorgopoulos, T.T. Dang, M.P. Schmid, T.R. Rizzo, Science, 302, 98 (2003)
Friday, 28 May 2004, 14.00 SISSA Room A
(Dipartimento di Fisica "A. Volta", Università di Pavia - INFM Pavia)
"Spin dynamics and spin-phonon effects in antiferromagnetic molecular rings"
Spin dynamics and spin-phonon effects in antiferromagnetic
molecular rings NMR has proved to be a powerful tool to
investigate both static and dynamic properties of magnetic
systems. In particular in recent years NMR has been
employed to study local spin dynamics in molecular magnets
and nowadays a considerable body of experimental results
are still unexplained.
Actually the nuclear spin relaxation process in a finite
system, with discrete energy levels, is a very general
problem and it requires coupling the spin system to
external degrees of freedom.
For this purpose we have investigated both spin correlation
functions and spin-phonon effects in antiferromagnetic (AF)
molecular rings, which are a subclass of molecular magnets.
Two parts of the work will be presented:
- AF ring coupled to adiabatic phonons. Lattice stability
is investigated for different values of the spin and
numbers of magnetic sites. The magneto-elastic transition
is shown to be heavily affected by the spin value,
displaying a qualitative difference in the nature of the
instability for the spin one-half.
- Spin dynamics at finite temperature and coupling to
We present results for the spin dynamics at finite
temperature, showing in particular how the low-frequency
dynamical correlation functions are influenced by the
Friday, 28 May 2004, 9.00 SISSA Room A
(Dipartimento di Fisica, Università Roma Tre - INFM Roma Tre and Democritos)
"Effects of confinement on static and dynamical properties of water"
Molecular dynamics results on water confined in a silica
pore are presented. Static and dynamical properties are
studied upon supercooling and by varying the hydration
level. Strong layering effects due to the hydrophilic
character of the substrate are found. At high hydration
levels a double dynamical regime is observed which
corresponds to the presence of two subsets of water
molecules with different static and dynamical properties.
In the low hydration regime, where most of the molecules
reside close to the substrate, the molecules show an
anomalous diffusion with a sublinear behaviour at long
time. This behaviour is strictly connected to the long time
decay of the residence time distribution analogously to
water at contact with proteins.
Tuesday, 18 May 2004, 11.00 SISSA Room D
(GlaxoSmithKline Medicines Research Centre, Computational and Structural Sciences, Stevenage - Hertfordshire, UK)
"Understanding the Glucocorticoid Receptor"
Friday, 7 May 2004, 11.00 SISSA Room A
(Department of Materials Science and Engineering, Massachusetts Institute of Technology)
"Electronic-enthalpy functional for first-principles simulations of finite systems under pressure(*)"
An electronic-enthalpy functional is introduced to allow
for the ab-initio simulation of finite systems under
pressure. Electrons are evolved according to a new operator
H+PV_q describing the "quantum" enthalpy of the finite
system, where H is the Hamiltonian of the system, P the
external pressure and V_q the quantum volume occupied by
the electronic cloud. The external pressure field acts
directly on the electronic structure of the system to
account directly for electrostatic and Pauli-repulsion
interactions through which, in real compression processes,
the external load is transferred to the particle. The
Hellman-Feynman theorem directly applies, and the ions
follow exactly an isoenthalpic dynamics. No external
pressurizing medium is required resulting in low
computational costs and straightforward implementations in
any electronic structure code. Thin coatings of
environmental ligands or ions can also be easily introduced
if chemically relevant. We applied this method to the study
of group-IV nanoparticles under shock waves, highlighting
the significant differences in the plastic and elastic
response of the diamond-cage under load.
(*) Work done in collaboration with Nicola Marzari and
Gerbrand Ceder (DMSE - MIT) and Francesco Mauri (LCPM-Paris
Wednesday, 5 May 2004, 11.00 SISSA Room E
(Max-Planck-Institut fr Festkörperforschung, Stuttgart)
"SUPRAMOLECULAR NANOARCHITECTURES AT SURFACES"
A key issue in nanotechnology is the development of
conceptually simple construction techniques for the mass
fabrication of identical nanoscale structures. Conventional
top down fabrication techniques are both energy intensive
and wasteful, because many production steps involve
depositing unstructured layers and then patterning them by
removing most of the deposited films. Furthermore,
increasingly expensive fabrication facilities are required
as the feature size decreases. The natural alternative to
the top down construction is the bottom up approach, in
which nanoscale structures are built from their atomic and
molecular constituents by self-assembly. This approach
relies on the exploitation of noncovalent directional
interactions and is one of the key building principles of
all living organisms.
Recent experimental advances have provided the unique
ability to investigate and manipulate individual
nanostructures on the atomic scale in a wide variety of
environments and under extreme conditions. In this talk I
will demonstrate the power of variable-temperature scanning
tunneling microscopy to probe the dynamics of
atomic/molecular motion and assembly. Scanned probes not
only allow us to image molecules adsorbed at surfaces with
unprecedented resolution but also to follow supramolecular
self-assembly and chemical complex formation in real space
and time. As examples we will discuss the building of
supramolecular nanostructures at surfaces by hydrogen and
coordination bonding. The steering of the self-assembly of
the molecular components allows for the fabrication of
distinct architectures. In particular the precise
positioning of molecules and metal centres on a surface
opens up new possibilities for the bottom-up fabrication of
low-dimensional functional materials.
Tuesday, 4 May 2004, 11.00 SISSA Room A
(Laboratory of Atomic and Solid State Physics, Cornell University)
"AB INITIO PREDICTIONS OF NANOSCALE RESONATORS"
In recent years, considerable experimental effort has gone
into the fabrication and characterization of resonators in
the nanometer range. Theoretical methods have proven to be
invaluable for understanding the results of these
experiments. In this talk, I will present two examples of
how we use various theoretical methods, including ab
initio, to study different aspects of oscillations and
mechanical loss in nanostructures.
One common defect in silicon devices is the divacancy.
Although the single vacancy in silicon is mobile at
fabrication temperatures, the divacancy is stable, and as a
result is one of the primary causes of mechanical loss. I
will present ab initio calculations of the elastic response
of this defect and show how these results can be used to
predict the mechanical loss caused by this defect in a
Recent experiments have demonstrated oscillations of a
suspended carbon nanotube under a gate voltage. We have
conducted simulations of such a system in which we treat
the nanotube as an elastic medium with parameters extracted
from ab initio calculations. I will show results from these
simulations, and show how they can be used to characterize
experimental devices for which several parameters, such as
length and diameter of the nanotube, are not known
Wednesday, 21 April 2004, 11.00 SISSA Room A
(Technical University Braunschweig)
"Thermodynamic properties of quantum Heisenberg models by a series expansion"
Using a high-temperature series expansion, thermodynamic
properties are analyzed for two different systems. (i)
Mixed-spin chain systems with alternating magnetic moments:
We focus on the difference between ferromagnetic (FM) and
antiferromagnetic (AFM) exchange. For the specific heat, we
find a multi-peak structure in the FM case which is
strongly enhanced as compared to that known for the AFM
case. Furthermore, we find indications of additional low
energy scales in the FM case which are not observed for AFM
exchange. (ii) SU(n) Heisenberg models represented by
exchange operators: In three dimensions, we obtain the
series coefficients as polynomials of n, and generalize n
to a continuous variable. We analyze singularities of a
correlation function, and report n-dependence of the
Tuesday, 30 March 2004, 16.30 SISSA Room A
(Università di Bologna)
"Stability and spectroscopical activities of lithium-doped carbon nanostructures: a computational study"
The capacity of lithium ion batteries depends strongly on the lithium storage
capacity of the carbon anode. In carbonaceous materials containing substantial
hydrogen (soft carbon), the amount of lithium that can be stored is larger
compared with pure graphite, and lithium appears to reversibly bind near
hydrogen atoms. Owing to their graphene-like structure combined with a
substantial hydrogen content, polycyclic aromatic hydrocarbons (PAHs) are
suitable models for soft carbon. Thus, in this work we present a computational
study on the stability and spectroscopical activities of a
large PAH: hexa-peri-hexabenzocoronene (HBC), C42H18 doped with alkali metals.
LinPAH complexes are investigated quantum chemically using the hybrid B3LYP
functional, a level of theory that has been shown to provide reliable results. We
explored a large number of lithium-interaction sites both above or above and
below the HBC molecule and obtained equilibrium structures, binding
energies and spectroscopical properties. It is shown that lithium
interaction does not simply causes charge transfer to the PAH but also covalent
bonding with the periphery of the hydrocarbon. Vibrational spectra of the
lithium complexes are also computed and compared with those of undoped HBC and it
is shown that remarkable changes in selected frequency regions can be
attributed to the presence of lithium atoms. UPS spectra corresponding to
di_erent degrees of lithium doping are also simulated and compared with
available experimental data.
Friday, 27 February 2004, 14.00 SISSA Room A
(Dip.to di Fisica, Università di Cagliari)
"Application of density functional theory to the superconducting state"
Thursday, 26 February 2004, 16.30 SISSA Room A
(Univ. de Paris 6)
"An approach of the chemical bond by the quantum topological analysis. Some applications to the first row transition metal compounds"
In point of view of the quantum mechanics the molecular
system is a collection of interacting particles (electron
and nuclei) and his behavior is ruled by the Schrdinger's
equation. The chemical bond isn't an observable and the
bonding properties are generally described by the
traditionally orbitals model. However, the pragmatic
conception of the chemist is linked to the Lewis picture
where the molecule is constituted by several atoms which
are connected by the chemical bonds. In addition, the bonds
are classified (covalent, ionic..) following the nature of
the atoms. In order to make a bridge between the two
approaches of the chemical bonding, we can propose an
alternative with the topological analysis of an local
electronic localization function which is calculated from a
wave function. Recently Richard Bader  (Atoms in
molecules) has proposed to use the electronic density ((r)
because it is an observable and it has a real physical
significant. However, the extrema values of ((r) are
essentially localized on atoms and its topological analysis
cannot distinguish lone pairs and the bonding pairs.
Another localization function has been proposed by Becke
and Edgecombe (ELF).  The topological analysis  of
the ELF function allows to share the molecular space which
is consistent with the traditional conceptions of Lewis and
VSEPR  models.
I will propose some recent applications of the topological
analyses (AIM and ELF) on a few transition metal systems
because the electronic structures of this kind of compounds
are generally not yet known. In this context, I will show
most results on the binary carbonyl complexes M(CO)
(M=Sc,..,Cu) . Another example of ELF topological
analysis will be presented with the system Cu2O22+ which is
involved in the life mechanisms.
- R.F. W. Bader. Atoms in molecules: A quantum theory. Oxford Univ. Press, 1990
- A. D. Becke and K. E. Edgecombe, J. Chem. Phys. 92:5397, 1990
- B. Silvi and A. Savin, Nature, 371:683, 1994
- R. J. Gillespie and P.L.A Popelier, Chemical bonding and Molecular Geometry From Lewis to Electron Densities, Oxford University Press, 2001
- J . Pilme, E. A. Alikhani and B. Silvi, J. Phys. Chem. A, 107: 4506, 2003
Thursday, 12 February 2004, 16.00 SISSA Room A
(Dipartimento di Scienze Chimiche - Università di Trieste)
"Time dependent Density Functional Theory of core electron excitations"
The Time Dependent Density Functional Theory (TDDFT) has
proven as a common and powerful method to study electronic
excited states. The basic equations of the methods will be
reviewed, with particular emphasis to their numerical
implementations in quantum chemistry computer codes, for
efficient molecular calculations in basis set formulation.
An extension of the method, suggested to study excitations
of core electrons, will be described, together with its
implementation in the ADF program. This extension includes
the most important physical effects of TDDFT which are
mandatory to describe excitations of 2p electrons of metal
atoms, keeping the numerical effort within reasonable
limits. This method is very promising to study large
systems like, for example, molecules of biological
interest, in particular regions of enzymes containing
transition metal atoms. Preliminary results on a series of
molecular models of the sulfite-oxidase enzyme obtained
with this method will be presented and compared with recent
Tuesday, 20 January 2004, 17.30 SISSA Room D
Michael L. KLEIN
(University of Pennsylvania)
"Computer Simulation of Self-assembling Systems: From Synthetic Di-block Copolymers to Natural Lipids."
The talk will review recent progress in using coarse grain
interaction models to follow the self
assembly in bulk solution of amphiphilic di-block
copolymers into a variety of structures, including
micelles, worms, and vesicles. The effect of polymer
molecular weight on the latter structure will
be discussed with emphasis on the properties of the bilayer
(membrane thickness, etc.). These
results will be contrasted with the behavior of naturally
occurring phospholipids membranes, the
self-assembly of which can also be demonstrated with coarse
grain models. The effect of a surface
on di-block copolymer self-assembly will also be discussed,
with particular emphasis on the
influence of the surface on the surfactant nanoscale
Friday, 12 December 2003, 11.00 SISSA Room A
Thursday, 27 November 2003, 16.00 SISSA Room A
(Universidad de Valencia)
"Droplets made of He-3 and He-4 atoms"
The talk presents a complete analysis of systems made of a
varying number of He-3 and He-4 atoms, with the objective
of determining a stability chart of such mixtures.
The computations are carried out by means of the Diffusion
Monte Carlo algorithm, using the Aziz potential.
The most remakable outcome is the prediction of instability
islands, which appear when the number of bosons is small. A
comparison with experimental measurements (preliminary) is
Thursday, 6 November 2003, 11.00 SISSA Room A
(University of Missouri at Columbia)
"Time-dependent spin density functional theory"
Time-dependent density functional generally suffers from an
ultra-nonlocality problem, namely the local density
approximation or the exchange-correlation potential always
fails, no matter how slowly varying is the density. I show
that this problem is particularly severe in time-dependent
spin density functional theory, but can be cured by
switching to a formulation in which the spin currents are
the basic variables. I discuss the physical significance of
the new terms that appear in the spin-current dependent
functional, and review the progress that has been made in
providing explicit expressions for the latter.
Friday, 17 October 2003, 12.00 SISSA Room A
(University of Rome La Sapienza)
"An evolutionary approach to the solution of the protein folding problem"
Monday, 22 September 2003, 15.30 SISSA Room C
(Università di Trieste)
"CeO2-based nanostructured materials: applications, open issues and perspectives"
CeO2 based materials are extensively employed in many
catalytic processes and particularly in the automotive
pollution control. Their role in the current TWCs will be
described. It will be shown that by designing the material
at an intimate - nanoscale - level some chemical and
physical properties can be properly tuned.
Thursday, 18 September 2003, 16.00 SISSA Room A
(Physics Department of the Université de Lausanne)
"Nanomatter probes for probing nanomatter: Photochemically grown silver nanoparticles with wavelength-controlled size and shape"
Matter organized at the nanometer scale has very
interesting properties that are not found either in bulk
matter or in its elemental components, atoms and molecules.
Since these peculiar properties arise from confinement
effect and interplay between surface and bulk effects, both
size and shape have a profound influence on the physical
and chemical properties of nanoparticles (NPs). Linear and
nonlinear optical properties, electronic and magnetic
properties, chemical reactivity and catalytic activity, all
show dramatic changes with these two parameters.
Correspondingly, an increasingly large interest has been
growing about controlling NPs size and shape by the
preparation method. Here we report a photochemical method
that transforms a colloidal solution of spherical silver
nanoparticles into a solution of larger nanoparticles with
different shapes. The photo-induced morphological changes
are highly wavelength-specific, resulting in particles with
size and shape that can be controlled by choosing the
wavelength(s) of the light used to drive the photochemical
growth. This method demonstrates that light can be used as
a convenient control parameter in the chemical synthesis of
Friday, 8 August 2003, 14.00 SISSA Room A
(Department of Physics, Tohoku University)
"Electron Correlation and Electron-Lattice Interaction in the High Tc Superconductivity"
It has been a long standing question whether a correlated
electronic model plane can explain the essential experiments
of superconductivity in cuprates. Although such a model has
been successful in explaining many physical properties, the
phonons and lattice effects are clearly present in these
materials. Recently, a kink structure is observed in the
angular resolved photoemission spectra (ARPES) around
50-80meV which is interpreted to originate from the coupling
of electrons with a half-breathing mode of the oxygen motion
in conjunction with the data of the neutron experiments.
We have investigated role of electron-phonon interaction in
the strongly correlated cuprates .
We have found that, by considering the off-diagonal
electron-phonon coupling, which modulates the transfer of the
Zhang-Rice singlet, the oxygen displacement contributes
strongest to the d-wave paring in the region along the
(00)-(qx,0) and (0,qy), where the strong coupling to the
electrons is observed experimentally. Being based on the
slave-boson picture applied to the t-J model and the Eliashberg
theory, role of electron-phonon interaction in ARPES, tunneling
spectra and optical conductivity is investigated. The vertex
correction is essential to describe the electron-phonon
interaction in the strongly correlated cuprates.
 Z.-X. Shen, A. Lanzara, S. Ishihara, N. Nagaosa, Phil. Mag. B 82 1349 (2002).
Tuesday, 29 July 2003, 11.00 ICTP Seminar Room, 1st floor
V. I. Anisimov
(Institute for Metal Physics, Yekaterinburg, Russia)
"Dynamical Mean-Field Theory for realistic systems"
LDA+DMFT is a novel computational technique for ab initio
investigations of real materials with strongly correlated
electrons, such as transition metals and their oxides. It
combines the strength of conventional band structure
theory in the local density approximation (LDA) with a
modern many-body approach, the dynamical mean-field theory
(DMFT). In the last few years LDA+DMFT has proved to be a
powerful tool for the realistic modelling of strongly
correlated electronic systems.LDA+DMFT method was
successfully used for description of the Mott-Hubbard
metal-insulator transition in the transition metal oxide
V2O3 and the alpha-gamma transition in the 4f-electron
Tuesday, 15 July 2003, 16.00 SISSA Room C
(Osaka University, Japan)
"Quantum phase transitions in the orthogonal-dimer spin system"
Frustrated quantum spin systems have attracted current interest.
A typical example is the orthogonal-dimer compound SrCu2(BO3)2,
where novel magnetic properties were observed such as magnetization
plateaus, excited states without dispersion. More recently, a new
orthogonal-dimer compound Nd2BaZnO5 was synthesized, where the local
moment J=9/2 shows an antiferromagnetic order below TN=2.4K. In this
talk, we discuss how a higher spin generalization (S>1/2), together
with the competing exchange couplings, affects the ground state
properties of the orthogonal-dimer spin systems.
Wednesday, 9 July 2003 - 16.00 ICTP SEMINAR ROOM - MAIN BUILDING (first floor)
"Electron transport with dissipation in molecular wires"
It is usually assumed that electron transport in molecular wires is ballistic
and that scattering with phonons is only important to thermalize the electrons
in the substrate far from the molecular contact. Here I discuss an alternative
formulation in which both tunneling and dissipation are explicitly taken int
account. In this approach electrons are accelerated by an external electric
field, but coupling to a heat bath prevents the electrons from moving far out
of equilibrium. Many-electron dynamics is treated within time-dependent
current-density functional theory, while dissipative effects are treated
phenomenologically by a master equation. The approach is well suited to
numerical simulations and allows us to study steady state and dynamical
phenomena. In particular, in the case of a simple double-barrier resonant
tunneling structure, I discuss how dissipative effects and the approximations
made in the master equation affect the calculated electric current.
Tuesday, 8 July 2003, 16.00 SISSA Room A
(Istituto Nazionale per la Fisica della Materia c/o Università degli Studi di Roma "La Sapienza")
"Solvent structure and impurity dynamics in doped Helium clusters"
Recent developments in Helium nanodroplet isolation spectroscopy witness increasing
interest in studying the properties of the cluster as a function of the number of
solvent atoms. Microwave and/or infrared spectral lines, assigned to doped clusters
with given number of Helium atoms in the range from unity to about ten, offer insight
into the structure of the first solvation shell and show evidence for the onset of
Quantum monte Carlo simulations, based on accurate interparticle potentials, are used
to enrich the picture inferred from experiments. We present a study of OCS@He_N, as
well as preliminary results on CO@He_N. For the former we relate the rotational
spectrum of the solvated molecule with the structural properties of the He atoms, and
both with the onset of superfluidity.In the case of CO@He_N, the purely rotational
spectrum --not available from measurements-- is discussed in terms of the cluster
symmetry along the molecular axis.
Thursday, 3 July 2003, 16.00 SISSA Room A
Gian Paolo Brivio
(Istituto Nazionale per la Fisica della Materia and Dipartimento di Scienza dei Materiali, Universita` di Milano-Bicocca)
"Spectroscopic properties at a semi-infinite metal surface within the DFT framework"
Spectroscopic properties at a metal surface, either free or covered with adsorbates,
are investigated by solving the Kohn-Sham equation of DFT. We use a formalism, based
on the Green function embedding approach, which is able to take into account a
semi-infinite solid and hence to describe the continuous spectrum of the system .
We show results of CCV Auger spectra of adatoms on simple metals by using different
levels of approximation both for the substrate and the Auger rates . We find that
the Auger spectra are affected by the site of the adsorbed impurity, which may be a
subsurface or a chemisorption one, and mainly depend on the local electronic properties
of the interacting system. De-excitation spectra of a metastable He atom on
alkali-metals of low work function on which the CVV Auger process is the dominant one,
are also analysed and compared with available experimental data . Finally, starting
from the DFT Green function, we present a many-body GW approach to deal with
semi-infinite jellium and demonstrate the presence of a surface resonance peaked at
the position of the first image state .
- H. Ishida, Phys. Rev. B 63, 165409 (2001).
- N. Bonini, M.I. Trioni and G.P. Brivio, Phys. Rev. B 64, 035424(1-7) (2001).
- N. Bonini, G.P. Brivio and M.I. Trioni, Phys. Rev. B, in press (2003).
- G. Fratesi, G.P. Brivio and L.G. Molinari, cond-mat/0305344 (2003), G. Fratesi, G.P. Brivio, P. Rinke and R.W. Godby, Phys. Rev. B submitted (2003), cond-mat/0305678
Wednesday, 2 July 2003, 16.00 AM SISSA Room A
(Laboratoire de Mineralogie-Cristallographie de Paris, Universitè Pierre et Marie Curie)
"Calculation of 17O NMR parameters from first principles. Applications to silicates, crystalline polymorphs and glass"
17O NMR spectroscopy is a promising tool for the study of the microscopic structure of oxides.
17O is a quadrupolar nucleus and thus both chemical shiftand electric field gradient tensors can be exploited.
Until recently, the conventional approach to the theoretical interpretation of solid state NMR spectra was to approximate
the infinite solid by a cluster, but the comparaison with experiment is poor.
Here we will present GIPAW method which is able to simulate periodic solids without the cluster approximation and perform
first-principle calculation with pseudopotentials. We apply this method to SiO2 crystalline polymorphs and
perform the assignment of the spectra of the ferrierite zeolite. We also apply the method to an aluminosilicate glass
with calcium cation, and show the impact of the level of the 3d orbitals of calcium on the chemical shift of 17O.
Thursday, 19 June 2003, 11.00 AM SISSA Room A
(Center for Electron Microscopy - Laboratorio Nazionale TASC-INFM, Area Science Park, Trieste, Italy)
"Transmission Electron Microscopy: how to study the solid state at the highest spatial resolution"
Current efforts to develop nanostructured materials and devices are
stimulating the implementation of new experimental probes of the
structure and chemical composition of solids on the atomic scale. Over
the years, transmission electron microscopy (TEM) has widely
demonstrated its potential to study material structures with the highest
spatial resolution available. More recently, the combination of scanning
tunneling microscopy (STM) and high-angle annular dark-field imaging
(HAADF) in scanning transmission electron microscopy has shown promise
as an analytical tool that can provide /chemical/ information with
comparable atomic resolution. The results obtained in the last year at
the Center for Electron Microscopy will describe how different
experimental conditions during a TEM experiment has to be used to
achieve the relevant physical properties of a specimen.
last modified: 14.01.2010