plotting exciton wavefunctions with TDHF in VASP 6.5.0

[guyohad]

Dear VASP Developers and Users,

I am trying to understand whether the exciton wavefunction plotting feature described here: https://www.vasp.at/wiki/index.php/Plot ... vefunction is intended to support only GW-BSE calculations, or if it is also compatible for TDDFT calculations (using ALGO = TDHF).

I was able to successfully reproduce the hBN example for the GW-BSE case. However, when I perform TD-PBE or TD-HSE calculations with NBSEEIG = 2 and BSEHOLE = 0.0 0.0 0.0, I get CHG.xx files, but the resulting exciton wavefunction appears non-physical - the exciton wavefunction appears uniform and does not decay with distance.

I am using VASP 6.5.0, and I have attached the relevant files for reference.

Could you provide me with some details about this?

Thanks a lot,
Guy

[pedro_melo]

Dear Guy,

I see that you are trying to use a model dielectric function. I will be taking over this issue, but I would like to point out a couple of things:

• The model dielectric function is activated with LMODELHF

• This model is good only on isotropic systems, since the dependency of the dielectric function on a G-vector is assumed to be through |G|. Using this model is probably not a good idea on materials such as hBN.

• You need a couple more tags in your INCAR, namely AEXX, LMODELHF. Note that LHFCALC is set to .TRUE. if LMODELHF=.TRUE.

• For BN, a better value for HFSCREEN is 1.7. You can see some values for other materials here

Again, I am not entirely sure that this will work correctly for hBN, as the material is not isotropic. I will come back to you with more information once I am done running some more tests.

Kind regards,
Pedro