PW users: please read. Optical strengths warning!

Deals with issues related to computation of optical spectra, in RPA (-o c) or by solving the Bethe-Salpeter equation (-o b). Includes local field effects, excitons, etc.

Moderators: Davide Sangalli, andrea marini, Conor Hogan, myrta gruning

PW users: please read. Optical strengths warning!

Postby andrea marini » Fri Mar 20, 2009 11:02 am

When calculating optical properties a potentially relevant contribution comes from the non-local components of the pseudopotential. For a definition of this contribution please check, for example, section V (Eqs. 7,8 and 9) of this article .

In yambo this contribution is contained in the core databaes (n)s.kb_pp.
This database is extracted by default when using Abinit by the a2y interface.

The importance of this contribution depends on the specific system and on the strength of non-locality in the pseudopotentials. This article (Fig. 4 and 5) shows that there is a dramatic change in the optical absorption of d-metals due to the inclusion of this term. For s and p electrons this contribution depends on the specific systems (see here
for more details).

Unfortunately we have not yet coded this contribution in the p(w)2y(ambo) interface.

As a consequence PW users are strongly invited to perform a test calculation by using abinit to estimate the importance of this contribution for their specific system.
Andrea MARINI
Istituto di Struttura della Materia, CNR, (Italy)
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Re: PW users: please read. Optical strengths warning!

Postby chinaye » Mon Aug 24, 2009 10:00 am

Dear Sir,
if we use the full diagonalization method to solve the effective two-particle equation, dose the problem caused by the lost of the nonlocal part you mentioned above still exist? In other words, we calculate the macroscopic dielectric function on the basis of excitation energies and wavefunctions rather than using the velocity operator. Thank you very much.
Jianfei Ye, PHD
Shanghai Institute of Ceramic Chinese Academy of Science (SICCAS)
Email:jianfeiye@mail.sic.ac.cn
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Re: PW users: please read. Optical strengths warning!

Postby chinaye » Wed Aug 26, 2009 7:24 am

Dear developers,
if I use the runlevel "yambo -b -o b -y d" on the top of the Kohn-Sham electronic structure obtained by using the PWscf program, can the nonlocal contribution be included in the BSE calculation? Thank you very much.
I post again to make myself understood.
Jianfei Ye, PHD
Shanghai Institute of Ceramic Chinese Academy of Science (SICCAS)
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Re: PW users: please read. Optical strengths warning!

Postby Conor Hogan » Wed Aug 26, 2009 1:46 pm

Dear Jianfei (please dont forget to add you signature to all posts!),
The other developers may provide a more complete/correct answer when they return from holidays, but for now let me just say that the problem should remain in the BSE calculation, since the screening matrix at q->0 will always be affected by this problem (in the head and wings - i.e. where the dipole matrix elements enter). You can do a test to see the magnitude of the effect by using the LiF databases included in the tutorial, and try a BSE calculation with and without the ns.kb_pp file inside the SAVE directory - the nonlocal term is quite large in LiF.
hope it helps for now!
regards
Conor
Dr. Conor Hogan
CNR-ISM, via Fosso del Cavaliere, 00133 Roma, Italy;
Department of Physics and European Theoretical Spectroscopy Facility (ETSF),
University of Rome "Tor Vergata".
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Re: PW users: please read. Optical strengths warning!

Postby andrea marini » Tue Sep 01, 2009 4:08 pm

chinaye wrote:Dear developers,
if I use the runlevel "yambo -b -o b -y d" on the top of the Kohn-Sham electronic structure obtained by using the PWscf program, can the nonlocal contribution be included in the BSE calculation? T


No. Using PWscf, at the moment, the nonlocal contribution is not included.
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Re: PW users: please read. Optical strengths warning!

Postby andrea marini » Tue Sep 01, 2009 4:11 pm

chinaye wrote:if we use the full diagonalization method to solve the effective two-particle equation, dose the problem caused by the lost of the nonlocal part you mentioned above still exist?


Whatever method you use to solve the two-particle equation you do not get the nonlocal part of the commutator, because it relies in the correct definition of the velocity operator.

chinaye wrote:In other words, we calculate the macroscopic dielectric function on the basis of excitation energies and wavefunctions rather than using the velocity operator. Thank you very much.


Sorry, but I do not understand what you mean. What is the relation between the basis you use to calculate the dielectric function and the definition of the velocity operator ?
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Re: PW users: please read. Optical strengths warning!

Postby Davide Sangalli » Sat Mar 16, 2013 4:39 pm

There pw users, this issue is now solved.

With the last GPL yambo revision, the commutator with the non local part of the pseudo-potential is now included in the calculation. In orther to obtiain that you just need to run

p2y -c -F data-file.xml

when you import your PWscf data-bases.
Check that p2y creates the database (n)s.Vnl .

The effect of this contribution has been tested also on "d-metals" computing the (magneto)optical properties of iron, cobalt and nickel
(Phys. Rev. B 86, 125139 (2012) ),

Davide
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
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Re: PW users: please read. Optical strengths warning!

Postby vence » Fri Nov 07, 2014 10:38 am

Davide Sangalli wrote:There pw users, this issue is now solved.
you just need to run

p2y -c -F data-file.xml

when you import your PWscf data-bases.
Check that p2y creates the database (n)s.Vnl .

Davide


Dear YAMBO developers,
p2y has no " -c " option in release version 3.4.1 and in current SVN version (rev 63). Is it now possible to include the non-local part contribution in the calculation?
Dr. Vyacheslav Sokolov
Fiber Optics Research Center, Russian Academy of Sciences
Moscow, Russia
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Re: PW users: please read. Optical strengths warning!

Postby Daniele Varsano » Fri Nov 07, 2014 10:44 am

Dear Vence,
please fill your signature with your complete affiliation. This is a rule of the forum.
The non local part of the pseudopotential should be now included automatically without specifying any option.
After running the p2y interface you should have ns.kb_pp_pwscf* files in your ./SAVE directory.

Best,

Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
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Re: PW users: please read. Optical strengths warning!

Postby vence » Fri Nov 07, 2014 11:05 am

Dear Daniele, thank you for your prompt reply.
Sorry for empty signature.
Dr. Vyacheslav Sokolov
Fiber Optics Research Center, Russian Academy of Sciences
Moscow, Russia
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