[Pw_forum] analysis of TDDFPT results

Sergi Vela sergi.vela at gmail.com
Fri May 20 15:01:57 CEST 2016

Dear Iurii and Dario,

Thanks for your answers. At some point I gave up with the Davidson code
since it was impossible to converge even just one excited state, this is
why I switched to Lanczos. I had some hope on being able to understand the
peaks but now I see that I've to try again with Davidson.

All my best,

2016-05-20 11:07 GMT+02:00 dario rocca <roccad at gmail.com>:

> Dear Sergi,
> I would like just to add that in the examples folder of the turboTDDFT
> code you can find examples on
> how to perform the Davidson diagonalization.
> Best,
> Dario Rocca
> On Fri, May 20, 2016 at 11:00 AM, Timrov Iurii <iurii.timrov at epfl.ch>
> wrote:
>> Dear Dr. Sergi Vela,
>> With the current implementation of the Lanczos algorithm in the
>> turboTDDFT program it is not possible to perform analysis of the origin of
>> individual peaks in the absorption spectrum. However, such an analysis can
>> be done using another flavor of the turboTDDFT code, namely the
>> turbo_davidson.x program. More information can be found in this
>> publication:
>> X. Ge, S. J. Binnie, D. Rocca, R. Gebauer, and S. Baroni, "turboTDDFT
>> 2.0—Hybrid functionals and new algorithms within time-dependent
>> density-functional perturbation theory", Comput. Phys. Commun. 185, 2080
>> (2014).
>> With the so-called turboDavidson code (turbo_davidson.x) you can
>> compute  the absorption spectrum (the same as with Lanczos) but as a
>> plus in the output file you will find the information about the origin of
>> the peaks (from which occupied level to which empty level there was a
>> transition and what is the corresponding intensity etc.). However,
>> if you are interested in computing the spectrum in a very
>> wide energy range, then turboDavidson becomes too expensive, and hence it
>> is recommended to use the Lanczos algorithm (at the cost described above,
>> i.e. no information about the origin of the peaks).
>> HTH
>> Best regards,
>> Iurii
>> --
>> Dr. Iurii Timrov
>> Postdoctoral Researcher
>> Swiss Federal Institute of Technology Lausanne (EPFL)
>> Laboratory of Theory and Simulation of Materials (THEOS)
>> CH-1015 Lausanne, Switzerland
>> +41 21 69 34 881
>> http://people.epfl.ch/265334
>> ------------------------------
>> *From:* pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on
>> behalf of Sergi Vela <sergi.vela at gmail.com>
>> *Sent:* Friday, May 20, 2016 10:30 AM
>> *To:* PWSCF Forum
>> *Subject:* [Pw_forum] analysis of TDDFPT results
>> Dear QE users and developers,
>> I've successfully performed a TDDFPT (Lanczos approach) calculation on a
>> system of my interest, and now I would like to analyze the different bands
>> of the resulting spectrum. I would like to ascribe them to chemical
>> (orbital-excitations, charge-transfer) processes such as I would do when
>> using standard TDDFT codes.
>> I'd like to know if this is indeed possible and, if so, I'd appreciate
>> some information on how to do it.
>> All my best,
>> Dr. Sergi Vela,
>> Laboratoire de Chimie Quantique, Universitè de Strasbourg, France
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