Electron Energy Loss Spectrum

[oliver_conquest]

To whom it may concern,

We want to calculate electron energy loss spectra (EELS) along a specific path (e.g. G-M-K) using VASP. The EELS requires the q-dependant dielectric function which according to this VASP wiki page (https://www.vasp.at/wiki/index.php/Cate ... properties) can be calculated using the ALGO = CHI or ALGO = BSE methods. I have a few of questions about obtaining EELS from VASP:

1. I ran the tutorial calculation for SiC from the wiki (https://www.vasp.at/wiki/index.php/Diel ... ies_of_SiC), see attached SiC_tutorial.zip folder, and it only prints the dielectric function for q = 1 (see OUTCAR.CHI), all other q-points indicate they are calculated but are not output.
Is it possible to output the dielectric function for all q-points using ALGO = CHI?

2. I also came across the new KPOINT_BSE tag which allows for calculation of the dielectric function using the BSE method at a specific q-point.
Can KPOINT_BSE or any other tag/method take a list of q-points and calculate the dielectric function? or would we have to use a script to calculate our dielectric functions for the list of q-points along our path?
Also, is it possible to use KPOINT_BSE with ALGO = CHI?

Kind regards,
Oliver

[martin.schlipf]

I believe KPOINTS_BSE is the way to go. Consider this subsection for an example input file. As far as I can tell, the output is only written to xml/hdf5 and not to OUTCAR.

I will inquire to get more information about this particular technique and see which methods it should be compatible with.

[oliver_conquest]

Many thanks!

Kind regards,
Oliver

[oliver_conquest]

Dear Martin,

Just following up if you've had a chance to inquire about which methods this technique can be applied?

Kind regards,
Oliver

[martin.schlipf]

Thank you for the reminder. I did get the feedback that at this stage BSE and TDHF are the only way to get finite q dielectric functions. As mentioned above, you use KPOINTS_BSE to do that.