[Pw_forum] Details on "third order derivatives not implemented with GGA" error

[Duy Le]

FYI.
There is NO truncation on the mailing list, we got all what you sent.
You gmail did it. Click Show Quote Text for full email.

--------------------------------------------------
Duy Le
PhD Student
Department of Physics
University of Central Florida.

"Men don't need hand to do things"


On Tue, Nov 9, 2010 at 9:02 PM, Brad Malone <brad.malone at gmail.com> wrote:

> No idea why it is being truncated, so this time I'll start the email after
> the error message
> ---------------
> From the forums:
>
> http://www.democritos.it/pipermail/pw_forum/2008-September/010123.html
> http://www.democritos.it/pipermail/pw_forum/2010-February.txt
>
> I understand that the third derivatives were never implemented and
> that only the LDA part was calculated, for the Perdew Zunger
> parameterization. Is this third derivative the third derivative that
> is mentioned in the routine PH/raman_mat.f90 (i.e, the third
> derivative of the energy with respect to the atomic displacements and
> with respect to two electric fields, as described in Lazzeri and
> Mauri, PRL 90,036401)?
>
> I am interested in getting a feel for what would be needed to
> implement the third derivatives with GGA into the code, as well as
> what sort of errors one might expect when using the third-order term
> as currently coded with LDA pseudopotentials (comments in the forums
> have hinted that the errors are likely small).  The shift in the Raman
> spectra for cd-Si is pretty minor when using a GGA pseudo compared to
> that of an LDA calculation, but I wanted to be able to quantify the
> error better for other systems where comparing the GGA raman spectra
> to one calculated within LDA was not possible (e.g., when the system
> doesn't exhibit a gap in LDA).
>
> Thanks for the help!
>
> Best,
> Brad
> UC Berkeley
>
>
> On Tue, Nov 9, 2010 at 5:59 PM, Brad Malone <brad.malone at gmail.com> wrote:
>
>> It appears that my last email was severely truncated on the mailing list
>> (even though it looks fine in my outbox). Below is what is should have been:
>> -----------------------
>> Hi, I am seeking more information on the error
>>
>> > from phq_setup : error # 1
>> > third order derivatives not implemented with GGA
>>
>> From the forums:
>>
>> http://www.democritos.it/pipermail/pw_forum/2008-September/010123.html
>> http://www.democritos.it/pipermail/pw_forum/2010-February.txt
>>
>> I understand that the third derivatives were never implemented and
>> that only the LDA part was calculated, for the Perdew Zunger
>> parameterization. Is this third derivative the third derivative that
>> is mentioned in the routine PH/raman_mat.f90 (i.e, the third
>> derivative of the energy with respect to the atomic displacements and
>> with respect to two electric fields, as described in Lazzeri and
>> Mauri, PRL 90,036401)?
>>
>> I am interested in getting a feel for what would be needed to
>> implement the third derivatives with GGA into the code, as well as
>> what sort of errors one might expect when using the third-order term
>> as currently coded with LDA pseudopotentials (comments in the forums
>> have hinted that the errors are likely small).  The shift in the Raman
>> spectra for cd-Si is pretty minor when using a GGA pseudo compared to
>> that of an LDA calculation, but I wanted to be able to quantify the
>> error better for other systems where comparing the GGA raman spectra
>> to one calculated within LDA was not possible (e.g., when the system
>> doesn't exhibit a gap in LDA).
>>
>> Thanks for the help!
>>
>> Best,
>> Brad
>> UC Berkeley
>>
>> On Tue, Nov 9, 2010 at 5:00 PM, Brad Malone <brad.malone at gmail.com>wrote:
>>
>>> Hi, I am seeking more information on the error
>>>
>>> > from phq_setup : error # 1
>>> > third order derivatives not implemented with GGA
>>>
>>> From the forums:
>>>
>>> http://www.democritos.it/pipermail/pw_forum/2008-September/010123.html
>>> http://www.democritos.it/pipermail/pw_forum/2010-February.txt
>>>
>>> I understand that the third derivatives were never implemented and
>>> that only the LDA part was calculated, for the Perdew Zunger
>>> parameterization. Is this third derivative the third derivative that
>>> is mentioned in the routine PH/raman_mat.f90 (i.e, the third
>>> derivative of the energy with respect to the atomic displacements and
>>> with respect to two electric fields, as described in Lazzeri and
>>> Mauri, PRL 90,036401)?
>>>
>>> I am interested in getting a feel for what would be needed to
>>> implement the third derivatives with GGA into the code, as well as
>>> what sort of errors one might expect when using the third-order term
>>> as currently coded with LDA pseudopotentials (comments in the forums
>>> have hinted that the errors are likely small).  The shift in the Raman
>>> spectra for cd-Si is pretty minor when using a GGA pseudo compared to
>>> that of an LDA calculation, but I wanted to be able to quantify the
>>> error better for other systems where comparing the GGA raman spectra
>>> to one calculated within LDA was not possible (e.g., when the system
>>> doesn't exhibit a gap in LDA).
>>>
>>> Thanks for the help!
>>>
>>> Best,
>>> Brad
>>> UC Berkeley
>>>
>>
>>
>
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