[Pw_forum] minimization in CP molecular dynamics

Brandon Wood brandonw at MIT.EDU
Fri Jul 11 03:56:27 CEST 2008


Dear Mansoureh and Nicola,

If memory serves, the values printed at the end of the file represent 
averages throughout the course of the simulation rather than final 
values.  So ekinc <> 0 is actually expected, unless you start from an 
already converged electronic configuration (although your value is still 
surprisingly high).  It also means the total energy doesn't accurately 
represent your final configuration.

A better thing to do is to take a look at the data output for the 
_final_ CP timestep in your run.  If ekinc is still nonzero at that 
timestep, increase nstep.  In any case, it is much more efficient to use 
CG minimization.

Brandon

----------------------------------------------------------
Dr. Brandon C. Wood
NSF Postdoctoral Fellow, Theoretical Sciences Unit
Jawaharlal Nehru Centre for Advanced Scientific Research
Bangalore, India
----------------------------------------------------------

Nicola Marzari wrote:
> 
> Shouldn't ekinc be zero ? I forgot the name used, but in a properly
> executed CP calculation, in which you do damped dynamics on the
> electrons to reach the ground state at fixed ions, the kinetic energy
> of the electrons (as opposed to the quantum kinetic energy of your
> system, ekin) should be zero.
> 
> I suggest to anyone learning CP calculations (a very worthy
> endeavour, and one that would be extremely useful in the long
> run) to study carefully the review paper on the topic by Marx and
> Hutter,
> 
> http://www.theochem.ruhr-uni-bochum.de/research/marx/marx.pdf
> 
> CP in Q-E now can also do conjugate gradients minimization on
> the electrons (more efficient than damped dynamics) and, for
> metals, ensemble-dft (i.e. born-oppenheimer dynamics).
> 
> For cg/edft, there was one bug (memmory misallocation)
> for parallel execution, just found by by Brandon Wood. It'll
> be fixed in the cvs in the next few days.
> 
> 
> 			nicola
> 
> Mansoureh Pashangpour wrote:
>> Dear Paolo
>> I know one of them is in Ry and another one in Ha,but when I compare 
>> them they are different
>> scf:  total energy              =  -243.33284101 Ry
>>
>> CP:  ekinc         :       10.67409      10.67409 (AU)
>>    ekin          :      153.58930     153.58930 (AU)
>>    epot          :     -458.58466    -458.58466 (AU)
>>    totel energy  :     -258.18270    -258.18270 (AU)
>>    temperature   :        0.00000       0.00000 (K )
>>    enthalpy      :     -258.18270    -258.18270 (AU)
>>    econs         :     -258.18270    -258.18270 (AU)
>>    pressure      :       -3.47982      -3.47982 (Gpa)
>>    volume        :      488.11442     488.11442 (AU)
>> Thanks
> 


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