questions about two-dimensional polarizability alpha_2D

[HaozheLi]

Dear Daniele,

I did a small test. All the scf/nscf input and out files are attached. This material has four types of atoms, and i considered soc effect in scf and nscf calculations.

Best wishes,
Haozhe

qe.zip

psuedopotential_Ti and_Mo.zip

psuedopotential_O_and_C.zip

[Daniele Varsano]

Dear Haozhe,

I was not able to reproduce your error. I did a test reducing a lot the QE parameter to speed up the calculation.
The results I get are reasonable.

What I did in QE:
Reduce the parameter as.
ecutwfc = 20 Ry
use the default diagonalization and not "cg"
k points 5 5 1
in nscf I considered 70 bands.

input and output of Yambo are attached.

I suggest you:
1) be sure to have the last release of Yambo
2) Try to reproduce the minimal test I did and see if you get weird results or not.

Best,
Daniele

[HaozheLi]

Dear Daniele,

Thanks for your suggestions and patient help. I upgraded my yambo to the latest version, and I got the reasonable results.
By the way, back to the polarizability alpha_2D, I noticed that using different number of bands (BSEBands) in the BSE calculation (in my case, i tested 1 valence band+1 conduction band, 2 valence bands+2 conduction bands and 3 valence bands+3 conduction bands) , I got the same exciton energy, which might mean that the calculation reached convergence. But alpha_2D in the o.alpha_q1_diago_bse for those three calculations are very different.
So does this mean that the alpha_2D in BSE calculation only comes from the contribution of the bands (BSEBands) we considered?

Best wishes,
Haozhe

[Daniele Varsano]

Dear Haozhe,

the real part of the polarisability has a lower convergence of the Imaginary part. You can realise it looking at the Kramers-Kroning relation between real and imaginary part. The static value of the real part depends on all the energy range of the imaginary part.

Best,
Daniele

[HaozheLi]

Dear Daniele,

Thanks a lot for your explanations.
Is there any way we can extract the screened coulomb interaction W （like Extended Data Fig. 1 of paper Nature Nanotechnology volume 15, 367–372 (2020)） using yambo or yambopy?

Best wishes,
Haozhe

[Daniele Varsano]

Dear Haozhe,

this can be done reading the nbd.em1s and ndb.cutoff databases, and yes can done using yambo-py.
Best,
Daniele