Anisotropic material and direction of applied electric field

[haseebphysics1]

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,

[Daniele Varsano]

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

[haseebphysics1]

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,

[Daniele Varsano]

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

[haseebphysics1]

Thanks very much!