[Pw_forum] reusing converged density

[Stefano Baroni]

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)
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
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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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