[Pw_forum] setting grid size and memory management for pw scf

[Mike Marchywka]

----------------------------------------
> From: giannozz at democritos.it
> Date: Fri, 11 Jan 2013 23:01:13 +0100
> To: pw_forum at pwscf.org
> Subject: Re: [Pw_forum] setting grid size and memory management for pw scf
>
>
> On Jan 11, 2013, at 17:06 , Mike Marchywka wrote:
>
> > Sorry if there is a simple answer but I could not immediately
> > figure out the
> > issues with setting fft grid size or the actual parameters to set
> > in the input file
>
> which issues?

http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node19.html
Manually setting the FFT grids to a desired value is possible, but slightly tricky, using input variables nr1, nr2, nr3 and nr1s, nr2s, nr3s. The code will still increase them if not acceptable. Automatic FFT grid dimensions are slightly overestimated, so one may try very carefully to reduce them a little bit. The code will stop if too small values are required, it will waste CPU time and memory for too large values.


In any case using CG diagonalization got it to run much faster, presumably making the point that memory can be more important in speed than just
counting operations ( I understand the default is faster with infinite memory).  Could not bracket Fermi level though, I'll have to check the
other settings for this. The system is just all trans retinoic acid with a single Fe atom either near the COOH or out of plane of the chain.
It I started with a a random placement and did structure optimization with jdftx but wanted to compare to QE and get more insight.
I'm not even sure this system has physical meaning ( the pseudopotentials are the first ones I found without a lot of consideration and I have
to come up with some "known" results for comparison yet). 


Thanks.



>
> P.
> ---
> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
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