Yambo Community Forum

Dear Claudio,

Hi, I would like to simulate the SHG properties of WTe2 which is a kind of Type II Weyl Semimetals, and it will be treated as a metallic system in the simulation with Yambo because there is a small overlap of the band structure at about 0.05 eV. However, it seems that the yambo_nl will use covariant dipole methods, which is not implemented for metal.

Followings are some methods that I have tried but cannot help:

1. I used “yambo_nl -V nl” to turn off the ”UseDipoles: Use Covariant Dipoles (just for test purpose)”, in this way, the simulation can proceed but the results are totally strange.

2. I also tried to use the “occupations = fixed” instead of “smearing” to force the system to semiconductor when doing the PWSCF, it helps in monolayer structure with small k points, but it cannot work in a high convergence system and bilayer structure.

3. Moreover, I tried to use shifted k points like “14 14 1 1 1 0” in the PWSCF to get a semiconductor result. However, it cannot help in the bilayer system, and the covariant dipole method cannot implement for shifted k points as well.

Is there other method to do the SHG simulation of the metallic system?

Best Regards,

Yubei

Dear Yubei

in fact the approach implemented in Yambo does not work with metals.

There are two possibilities:

1) you can try with another code, for example 2light
https://etsf.polytechnique.fr/Software/Ab_Initio

2) I can modify yambo_nl to work with shifted grids,
and let you know

best
Claudio

Dear Claudio,

Thank you very much for your suggestion.

I will try with other code first and wait for the modification of yambo_nl.

Thanks again for your help.

Best Regards,

Yubei

Dear Yubei

you can use Yambo_nl with shifted grids
if you remove the line

call error(' Shifted grids not implemented yet in covariant dipoles ')

in the file:
src/bz_ops/k_map_nearest_by_dir.F

and then works without symmetries, namely
you put in the QE file

noinv=.true.
nosym=.true.

best
Claudio

Dear Claudio,

Thank you very much for your help.

I will have a try.

Best Regards,

Yubei