[gpaw-users] GPAW dev r7883: Spin-pol vdW-DF2 diverges

[Duy Le]

Dear all,
I just joined a little discussion on the spin-polarized vdW-DF at
PWscf forum.  Timo Thonhauser had short input but I think it is very
valuable for someone who uses or implements spin-polarized vdW-DF. See
below.
--------------------------------------------------
Duy Le
PhD Student
Department of Physics
University of Central Florida.

"Men don't need hand to do things"


---------- Forwarded message ----------
From: Stefano de Gironcoli <>
Date: Fri, Apr 29, 2011 at 3:49 AM
Subject: Re: [Pw_forum] vdW functional not implemented for spin polarized runs
To: pw_forum
Cc: Thonhauser Timo


Dear all,

    I inquired Timo Thonhauser (now Wake Forest  University), the main
character behind the vdW-DF functional implementation in Quantum
ESPRESSO,  about the issue of the spin-polarized version of vdW-DF.

I'm reporting his opinion below:

"In general, at the moment there exists NO true extension of vdW-DF for
spin-polarized cases. Several groups have expressed interest in working
on it, but nothing has been published yet. Note that just evaluating
vdW-DF for the two spin densities separately, while simple to implement,
is an approximation which is difficult to justify: there is no
quantitative measure of the error being made, other than hand waving
arguments that it has to be small. Also, we did not implement that
simple fix, because we were afraid that people would use it as a
black-box for spin-polarized calculations, not knowing that there is no
spin-polarized vdW-DF"

hope this helps to clarify the situation.

stefano



On 04/27/2011 04:45 PM, Duy Le wrote:
> --------------------------------------------------
> Duy Le
> PhD Student
> Department of Physics
> University of Central Florida.
>
> "Men don't need hand to do things"
>
>
>
> On Wed, Apr 27, 2011 at 3:29 AM, Stefano de Gironcoli<degironc at sissa.it>  wrote:
>> the vdW energy depends on the local polarizability of the electron gas ..
>> does it depend on the spin density ? I would say so.
> I would depend as we expected, however, from the formalism of vdW-DF,
> spin is not taken into account. So, I think in the limit of vdW-DF,
> the spin-dependence is ignored.
>
>> Is it taken into account in the current definition of vdw-DF ? I would say
>> no...
>> how is it implemented in GPAW ? just blindly or with some argument ?
> I am not sure. Did not have a chance to look at it and there is no
> found document about this.
>
>> stefano
>>
>> On 04/27/2011 06:35 AM, WANG Wei wrote:
>>
>> Thank you for your advice, Deu. Yes, the non-local energy is independent the
>> spin density.
>>
>>
>> On 27 April 2011 12:34, Duy Le<ttduyle at gmail.com>  wrote:
>>
>> --------------------------------------------------
>> Duy Le
>> PhD Student
>> Department of Physics
>> University of Central Florida.
>>
>> "Men don't need hand to do things"
>>
>>
>>
>> On Tue, Apr 26, 2011 at 1:00 PM, Stefano de Gironcoli<degironc at sissa.it>
>> wrote:
>>
>> Dear  WANG Wei
>>    the vdw-DF functional form is not defined for spin polarized system...
>>
>> Or it does mean that non-local energy is not spin-dependent but
>> charge-density-dependent only.
>>
>>    if you define, implement and test it, you could even get a nice
>> publication out of it. thank you.
>>
>> The spin-polarized vdW-DF has been implemented in GPAW.
>>
>> stefano
>>
>>
>>
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>>
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