Anisotropic material and direction of applied electric field

Deals with issues related to computation of optical spectra in reciprocal space: RPA, TDDFT, local field effects.

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haseebphysics1
Posts: 169
Joined: Sat Aug 17, 2019 2:48 pm

Anisotropic material and direction of applied electric field

Post by haseebphysics1 » Wed Feb 19, 2020 7:16 pm

Dear Yambo developers,

I have a confusion in case of anisotropic 3D bulk material and provided no special care was taken in experimental solution about the direction etc. how we should proceed in setting the following parameter!

% LongDrXd
1.000000 | 0.000000 | 0.000000 | # [Xd] [cc] Electric Field
%

Do we need to do all three directions [100], [010], [001] independently and then take the mean by (absx+absy+absz)/3 or do we have something better to do in this sort of situation?

And also I want to ask the difference between LongDrXd and ExtF_Dir parameters? Both do the same thing?

Thanks,
Haseeb Ahmad
MS - Physics,
LUMS - Pakistan

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Daniele Varsano
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Re: Anisotropic material and direction of applied electric field

Post by Daniele Varsano » Wed Feb 19, 2020 7:49 pm

Dear Haseeb,
Do we need to do all three directions [100], [010], [001] independently and then take the mean by (absx+absy+absz)/3 or do we have something better to do in this sort of situation?
It depends on what you are interested in, i.e. if you want to compare with experiments done with aligned sample and linear polarized light, then you want to select of the directions or to look at them independently, otherwise, you can average them, or alternatively choose a direction having components in all the directions [111].

LongDrXd : Direction of the perturbing electric field (not to be confused with the propagation direction).
ExtF_Dir is the direction of the external field in a non-linear optic calculation (yambo_nl).

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/

haseebphysics1
Posts: 169
Joined: Sat Aug 17, 2019 2:48 pm

Re: Anisotropic material and direction of applied electric field

Post by haseebphysics1 » Wed Feb 19, 2020 10:03 pm

Thank you for your answer.
you can average them, or alternatively choose a direction having components in all the directions [111]
In this case

% LongDrXd
1.000000 | 1.000000 | 1.000000 | # [Xd] [cc] Electric Field
%

will I get single column of mean absorption (automatically done by Yambo) or will I be able to see individual components also and doing the average myself?

Q2: I was wondering in TDDFT, BSE optical output file we also get IPA spectrum at the fourth column or so? while I have also calculated optical absorption explicitly at the RPA level (both with LFE and without LFE). So, should IPA column by
yambo -o c -k hartree results should match with yambo -o c -k lrc (fourth column IPA) results? Similarly in the BSE output file, IPA spectra also printed... It is same as we get RPA with IP approximation? Am I right?

Regards,
Haseeb Ahmad
MS - Physics,
LUMS - Pakistan

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Daniele Varsano
Posts: 4201
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

Re: Anisotropic material and direction of applied electric field

Post by Daniele Varsano » Wed Feb 19, 2020 10:08 pm

Dear Haseeb,
will I get single column of mean absorption (automatically done by Yambo) or will I be able to see individual components also and doing the average myself?
You will have a single spectrum calculated with an electric field having 1/sqrt(3)(i,j,k) direction.
Q2: So, should IPA column by yambo -o c -k hartree results should match with yambo -o c -k lrc (fourth column IPA) results?
Yes if all the input parameters (bands) are the same.
Similarly in the BSE output file, IPA spectra also printed... It is same as we get RPA with IP approximation? Am I right?
yes if you have inserted the same number of bands in the two calculations.

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/

haseebphysics1
Posts: 169
Joined: Sat Aug 17, 2019 2:48 pm

Re: Anisotropic material and direction of applied electric field

Post by haseebphysics1 » Wed Feb 19, 2020 10:25 pm

Thanks very much!
Haseeb Ahmad
MS - Physics,
LUMS - Pakistan

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