[DFTB-Plus-User] Am I fully optimizing the charges of my structure?

[Bálint Aradi]

Dear Alathea,

> I changed the angular momentum of oxygen to "p", ran a static relaxation 
> of the geometry to get the charges converged to 1e-5 tolerances, and 
> then read those charges into a script to generate the band structure. 
> Still, I get an error that the SCC does not converge in 1 iteration. I 
> have attached the log file and the input script here.

Please note, that in DFTB (as in DFT) the band structure calculation 
consists of two steps:

1. Sampling the Brillouin-zone with a good k-point sampling to obtain 
the correct density (charges) at the end of a well converged SCF (SCC) 
cycle.

2. Use the obtained well converged density to build up the Hamiltonian 
and obtain the eigenvalues in any k-points of interest (typically along 
high symmetry lines in the BZ) with a **single diagonalization*- 
(without SCF/SCC) convergence.

The reason for this procedure is, that the k-points along the 
high-symmetry lines typically give a very poor BZ sampling, so even a 
converged SCF/SCC won't give you a proper density/charges. This why the 
density from the first calculation used and only a single 
diagonalization (1 SCF/SCC step) is made.

Therefore, you don't have to reach SCC convergence in the 2nd 
calculation. See also the corresponding chapter of DFTB+ recipes:

https://dftbplus-recipes.readthedocs.io/en/latest/basics/bandstruct.html

Best regards,

Bálint


-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/

-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 840 bytes
Desc: OpenPGP digital signature
URL: <http://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/attachments/20220222/879a6567/attachment.sig>