Issues on convergence

Run-time issues concerning Yambo that are not covered in the above forums.

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Issues on convergence

Postby hplan » Wed Apr 22, 2009 5:06 pm

Dear Developers:

I have some questions about convergence. Taking FFTGvecs for example, we need do several tests on convergence and normalization to find a proper setting. When we do self-energy calculation, we can confirm convergence by checking QP gap with respect to FFTGvecs. My confusion is how can we confirm that the result is converged when we do response-calculation ? Is there any guideline for convergence testing ?

Another question is about normalization. Can we say that the output information below confirms wavefunctions are normalized ?
"
Code: Select all
[WF loader] Normalization (few states)  min/max  :0.364E-11  1.00

"
Thank you !
Best,
Hai-Ping LAN
Hai-Ping LAN,
Department Of Electronics,
Peking University, 100871,Beijing, CHINA
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Re: Issues on convergence

Postby Daniele Varsano » Wed Apr 22, 2009 5:15 pm

hplan wrote:Dear Developers:


Another question is about normalization. Can we say that the output information below confirms wavefunctions are normalized ?
"
Code: Select all
[WF loader] Normalization (few states)  min/max  :0.364E-11  1.00

"


Yes, this is the minimum and maximum of the scalar product between few states taken as representative.
The perfect situation should be 0.00 1.00, i.e. different states are orthogonal between each other, and
normalized to 1.00.
In your case it confirms your wfs are orthonormalized.

About your first question, as other parameter you have to check your absorption spectrum, energy-loss spectrum etc with
FFTGvecs, depending on the quantity you are interested in.

Hope it helps,

Best,

Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
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Re: Issues on convergence

Postby andrea marini » Wed Apr 22, 2009 8:59 pm

hplan wrote:I have some questions about convergence. Taking FFTGvecs for example, we need do several tests on convergence and normalization to find a proper setting. When we do self-energy calculation, we can confirm convergence by checking QP gap with respect to FFTGvecs. My confusion is how can we confirm that the result is converged when we do response-calculation ? Is there any guideline for convergence testing ?


Dear Hai-Ping LAN,

in general Daniele is right. Peek up your quantity (absorption, QP corrections,...) and change the input file parameters until you do not find the result is unchanged. Among all variables, maybe FFTGvecs is not the one that has a major impact on the calculated quantities. It defines the size of the FFT mesh. I'd leave as it is in the default unless you do not really want to speed up your calculation and/or to reduce the memory usage of your run.

When you do a response function calculation the key parameters are the number of bands in the electron-hole summation and the number of G-vectors used in the exchange/correlation part. Moreover you should do different runs with different meshes of k-points.

Hope it helps

Andrea
Andrea MARINI
Istituto di Struttura della Materia, CNR, (Italy)
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Re: Issues on convergence

Postby hplan » Fri Apr 24, 2009 10:41 am

Dear Andrea and Daniele,

Thank you for detailed instructions on this issue.
My resource is limited ,and large FFTGvecs need exhausted physical memory from my previous experience on self-energy calculations. This is the reason why i care about this parameter.
Hai-Ping LAN,
Department Of Electronics,
Peking University, 100871,Beijing, CHINA
hplan
 
Posts: 58
Joined: Thu Mar 26, 2009 2:26 pm


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