[Pw_forum] reusing converged density

[Luke Shulenburger]

Dear Stefano,

Thanks for the quick reply.  I think it probably best to stick with a
solution inside the code.  It sounds like everything is already there and my
job will more akin to plumbing than algorithm testing and validation.  I'll
take a look at it soon.  What is the proper way to submit code for review
once I get that far?

Luke
Geophysical Laboratory
Carnegie Institution of Washington
(lshulenburger at ciw.edu)


On Sun, Feb 28, 2010 at 4:17 AM, Stefano Baroni <baroni at sissa.it> wrote:

> Dear Luke:
>
> I am no longer familiar with the guts of the code, but I think this would
> require some coding. The problem is, the PW basis set (and the related FFT
> grids) slightly depends on the strain state. In variable-cell MD, this
> dependence is eliminated by using a "hard" cutoff that defines the PW basis
> set and a "smooth" one that implicitly, but continuously, eliminates some of
> the PWs according to the strain state. I can see two strategies that you may
> want to try.
>
> The first would probably require you to put your hands into PW: you simply
> have to make the "soft" cutoff option available to static scf calculations.
> I believe this should be rather easy, and I will ask some of the people who
> know the code well to assist you if you want to try.
>
> Second option. Do Fourier interpolation. Take the charge density /
> wavefunctions calculated and stored with one FFT grid and use a simple
> stand-alone program to calculate the fourier coefficients with respect to a
> different grid. Writing this simple code would not require any knowledge of
> the PW guts. If you want to give it a try, I can give you a few hints.
>
> If you decide to try either one of the above two approaches, I beileve the
> QE developers' team would be more than glald to help and to include your
> contribution in a future distribution of QE.
>
> Cheers
> Stefano B
>
> On Feb 28, 2010, at 3:33 AM, Luke Shulenburger wrote:
>
> Hello,
>
> I would like to calculate the ground state of a system with several
> different strains.  As the calculations are somewhat hard to converge, I was
> hoping that I could re-use the density and wavefunctions from one of the
> calculations as starting points of the others.  I know that the code does
> this under the hood when the geometry is changed in MD or geometry
> optimizations, but I cannot seem to get it to work for separate static scf
> calculations.   Is this feature available?
>
> Luke Shulenburger
> Geophysical Laboratory
> Carnegie Institution of Washington
> (lshulenburger at ciw.edu)
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>
> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
> http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) /
> stefanobaroni (skype)
>
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