Circular dichorism

[ahsan_javed]

Hi i have done circular dichroism (CD) using GW+BSE in VASP, and the CD that we obtain arises from the electric quadrupole and magnetic dipole contributions (as known from literature) and is in accordance with experimental CD from literature. I would like to know if it is possible to separate the contributions from the electric quadrupole and the magnetic dipole in the CD that I have calculated to see it's effect individually.

[fabien_tran1]

Hi,

Circular dichroism is not implemented in VASP. That probably means that you used an external package to calculate CD, right?

[ahsan_javed]

Playing with vasprun.xml form BSE using python script and following this work (Nature Communications| (2024) 15:2573)

[alexey.tal]

Dear ahsan_javed,

If I understood you correctly you use the dielectric function from vasprun.xml to compute the CD signal. However, if you are using the dielectric function in the q=0 limit, only the dipole approximation is used. Higher order terms are effectively included in the dielectric function at finite q, but not at q=0. Thus, I'm not sure I understand your question. Can you provide more detail on how you calculate CD?

Best wishes,
Alexey

[ahsan_javed]

Please find attached files from BSE step to have a better idea about my calculations. thanks

[ahsan_javed]

can you kindly comment on?

[alexey.tal]

Thank you for sending the files. From your python script I see that you plot the xx component of the dielectric function against the wavelength. So it is just the dielectric function, i.e., not the difference between left and right polarized light, which is required for CD. Also, as I said previously, at q=0 the dipole approximation is used for the calculation of the dielectric tensor, so magnetic dipole and electric quadruple terms are not included.