[Q-e-developers] Question on vdW-DF2 (rPW86)

[Riccardo Sabatini]

Dear Ikutaro,

     as Stefano told you we are working on this issue. In the SVN we 
have not done any modification yet, but as you pointed out changing 
iexch to 0 in the VDW-DF2 configuration will solve the problem.

     In the next days we'll decided if to keep the LDA part in the rPW86 
or modify the functional, but up to now the fastest solution is changing 
by hand the flag in the code and recompile.

     I'll be back to you as soon as we decide how to implement the fix, 
thanks again for the help.

     Best regards,

     Riccardo

On 6/27/11 7:21 PM, Stefano de Gironcoli wrote:
> dear Ikutaro Hamada,
>
> Indeed you are right.
>
> It should have  been fixed in the svn version..
> Riccardo: can you confirm it ?
>
> What we would actually like to do is to code as PW86 only the 
> correction to LDA exchange and leave iexch=1 but we are currently 
> testing the impact of this and there are some micro-differences we 
> would like to understand better...
>
> stefano
>
>
> Quoting ?? ??? <ikutaro at wpi-aimr.tohoku.ac.jp>:
>
>> Dear developers of quantum espresso,
>> (developers of vdW-DF in q-e)
>>
>> I have a question on vdW-DF2 implemented in quantum-espresso 4.3.1.
>> In vdW-DF2, the revised PW86 (subroutine rPW86 of flib/functional.f90)
>> exchange (igcx=13)
>> is used.  Because rPW86 already contains the LDA exchange energy and
>> potential,
>> it seems iexch should be set to 0, not 1 in Modules/funct.f90.
>>
>> I'm pleased if you let me know if I'm correct or not.
>>
>> Sincerely,
>>
>> Ikutaro Hamada
>>
>> ---
>> Ikutaro Hamada
>> WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku
>> University
>> 2-1-1 Katahira, Aoba-ku, Sendai 980-8577
>> Tel: +81-22-217-5938
>> Fax: +81-22-217-5941
>> E-mail: ikutaro at wpi-aimr.tohoku.ac.jp
>>
>>
>>
>>
>>
>>
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>
>
>
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-- 
Riccardo Sabatini | PhD Student in Condensed Matter
Scuola Internazionale di Studi Avanzati (SISSA)
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