[Pw_forum] ecutrho in phonon calculations

[elbuesta at icqmail.com]

 Dear Yuyang, 

If I may ask (I did not follow the discussion, only now I saw your e-mail, so I don't know what was discussed previously), what are the values of the "conv_thr" and "tr2_ph" parameters used in your case? I never did phonon calculations for your specific case, but using USPP for Ag/Cu/Au/Pt, the phonon frequencies are already converged at wfc and charge cutoffs of 40/480, as long as one performs a very accurate scf and phonon calculation. For silver, for example, I had to use a "conv_thr" as low as 10-12, and tr2_ph about 10-19.

Fabio Negreiros Ribeiro
Post-doc at CNR
Pisa - Italy
 

-----Original Message-----
From: YY <xrhino at gmail.com>
To: Paolo Giannozzi <giannozz at democritos.it>
Cc: pw_forum <pw_forum at pwscf.org>
Sent: Wed, Apr 18, 2012 5:26 pm
Subject: Re: [Pw_forum] ecutrho in phonon calculations


Hi Paolo,

Thanks for your reply.  For the phonon calculation, I use a PBE-US PP
(Fe.pbe-sp-van_ak.UPF, and Se.pbe-van.UPF).
According to your suggestion, I increase the ecutwfc, and do several
tests.  Unfortunately, it seems there are still convergence problem:

ecutwfc  ecutrho  f1(cm-1) ... f12(cm-1)
100        1200      106.5    ...  329.5
100        2400      127.2    ...  339.8
200        2400      127.8    ...  341.2
200        4800        32.9    ...  319.8

Could there be any other reasons to cause this convergence problem?

Yuyang at RPI

On Mon, Apr 16, 2012 at 11:52 AM, Paolo Giannozzi
<giannozz at democritos.it> wrote:
> On Thu, 2012-04-12 at 16:07 -0400, YY wrote:
>
>> But I find there is no simple convergence trend while increasing
>> ecutrho.  When I use 35 Ry ecutwfc, and fix all the other parameters,
>> the results are like this:
>>
>>    ecutrho       f1(cm-1)      ....  f12(cm-1)
>>    420            40.475                324.062
>>    600           123.746               350.727
>>    900           -251.876              306.721
>
> unfortunately in at least some [ and I am afraid, in many ] cases,
> a rather high cutoff is needed anyway to get decent phonons. If
> this happens, the advantage of using USPP becomes dubious, given
> their significant computational overhead wrt Norm-Conserving PPs.
> Which USPP did you use ?
>
> P.
>
> --
> Paolo Giannozzi, IOM-Democritos and University of Udine, Italy
>
>
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