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Dear all,<br>
<br>
Now, I know that the bad results of dielectric function relate the
pseudopotential(PP)!<br>
The PP I used is from abinit by fhi2upf.<br>
After that, I tested another qso PP, which is from <a
class="moz-txt-link-freetext"
href="http://fpmd.ucdavis.edu/potentials/index.htm">http://fpmd.ucdavis.edu/potentials/index.htm</a>
and <br>
<a class="moz-txt-link-freetext"
href="http://eslab.ucdavis.edu/software/index.htm">http://eslab.ucdavis.edu/software/index.htm</a>
. Using this PP, the profile of the dielectric function curve is
similar with the result from wien2k. But, this PP gives out somewhat
bad band structures!<br>
<br>
So, it confuses me that a PP which can give good band structure
results in bad dielectric function, while a PP which gives somewhat
bad band structure results in a dielectric function comparable with
wien2k. Can anyone give some explanations? (see attachments)<br>
<br>
Another question aslo confuses me as mentioned in the original
email: what's the meaning of the "plasmon frequency" given by
epsilon.x? And why it depends on the input parameter intrasmear and
even wmax?<br>
<br>
Best regards!
<br>
<br>
Liu Guibin
<br>
Postdoctoral Fellow,
<br>
Department of Physics,
<br>
The University of Hong Kong
<br>
<a class="moz-txt-link-abbreviated" href="mailto:gbliu@hku.hk">gbliu@hku.hk</a>
<br>
<br>
<br>
于 2011/7/7 17:39, gbliu 写道:
<blockquote cite="mid:4E157EEE.4050309@163.com" type="cite">Dear
all,
<br>
<br>
I want to calculate dielectric function of carbon nanotube,
but I have no experiences of calculating dielectric function
before. Hence, I decide to start with a simple case of fcc gold,
because there are referable results from wien2k (wien2k is capable
of simple case such as fcc Au, but too resource consumptive to
deal with large cells such as CNT).
<br>
Because epsilon.x doesn't support USPP, the UPF file of Au
is got by converting fhi file from abinit using fhi2upf.x. I
calculate fcc Au with a=7.71bohr and 15x15x15 k-mesh using both
pwscf(v4.3) and wien2k. First I check the band structures and find
that the results from both softwares agree well (see attachments).
But the results of epsilon from pwscf is not satisfactory as the
results from wien2k:
<br>
<br>
(1) Figures imag_eps and real_eps are the compares with only
interband contribution. (note that for pwscf, I subtract the
intraband contribution [-omega_p^2/omega^2] to get only interband
contribution for compares). We can see the differences are
notable. What's the reason? BTW, I use a homogeneous k-mesh also
15x15x15 generated by myself for epsilon calculation (see input
file fccAu.nscf4eps.in).
<br>
------input for epsilon.x--------
<br>
&inputpp
<br>
outdir='./work'
<br>
prefix='fccAu'
<br>
calculation='eps'
<br>
/
<br>
&energy_grid
<br>
smeartype='gauss'
<br>
intersmear=0.1d0
<br>
intrasmear=0d0
<br>
wmax=20d0
<br>
wmin=0d0
<br>
nw=600
<br>
shift=0d0
<br>
/
<br>
--------------------------------
<br>
<br>
(2) As for the intraband contribution, wien2k gives the
plasma frequency 9.0075eV which agrees well with experimental
value (ref: <a class="moz-txt-link-freetext" href="http://wave-scattering.com/drudefit.html">http://wave-scattering.com/drudefit.html</a>), but the
result from epsilon.x is puzzling.
<br>
Specifically, plasma frequency given in the output of epsilon.x is
dependent on the input parameters:
<br>
<1>. intrasmear=0, wmax=20d0 --> The bulk xx plasmon
frequency [eV] is: 14.877926200
<br>
<2>. intrasmear=0, wmax=10d0 --> The bulk xx plasmon
frequency [eV] is: 7.625822195
<br>
<3>. intrasmear=0, wmax=6d0 --> The bulk xx plasmon
frequency [eV] is: 3.156554381
<br>
<4>. intrasmear=0.1, wmax=20d0 --> The bulk xx plasmon
frequency [eV] is: 15.766403193
<br>
<5>. intrasmear=0.1, wmax=10d0 --> The bulk xx plasmon
frequency [eV] is: 9.322251787
<br>
<6>. intrasmear=0.1, wmax=20d0 --> The bulk xx plasmon
frequency [eV] is: 6.263713572
<br>
However, none of these values is the one got by fitting the
results using Drude model [ 1 - omega_p^2/(omega^2+i*omega*gamma),
gamma is the intrasmear here ]. By fitting the results using Drude
model, I get omega_p=5.528769eV, for all the cases above
(<1>~<6>). But this omega_p is far from the
experimental value (~9 eV)! What's wrong? And what are the
meanings of the values given in <1>~<6> ?
<br>
<br>
How can I get more accurate results like the ones from
wien2k?
<br>
Please help me if you know something about this, thanks in
advance!
<br>
<br>
Best regards!
<br>
<br>
Liu Guibin
<br>
Postdoctoral Fellow,
<br>
Department of Physics,
<br>
The University of Hong Kong
<br>
<a class="moz-txt-link-abbreviated" href="mailto:gbliu@hku.hk">gbliu@hku.hk</a>
<br>
<br>
<br>
<br>
<br>
<br>
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