[Pw_forum] graphene scf calculation

[Eyvaz Isaev]

Dear  Victor,


>  But scf calculation for graphene can't
> achieve convergence. I've tried different mixing_beta,
> mixing_mode, degaus ant ecutwfc. The example input file is
> attached. Could you please tell me which parameters I should
> tune to achieve convergence?

There are several issues (according to your input file) that can affect on convergence in your case. But the main reason, most likely, is k-mesh grid, using 16x16x1 grid the convergence was OK.

Please pay attention, 16x16x1, because you simulate  2D case. 

For Ultrasoft PsP you should use ecutrho about (8-12) times larger than ecutwfc. 

You have 2 carbon atoms with 4 valence electrons, so, you do not need 8 bands (only 4 is enough), if graphene is semiconducting. In this case you can omit degauss (not sure it is used, if you did not specify "occupations"  keyword). Otherwise use keywords specific for metallic case
(occupations='smearing', smearing='XYZ', degauss=LKJ).  

I used mixing_beta=0.1 and mixing_mode-'local-TF', too.

Bests,
Eyvaz.


-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com


--- On Wed, 11/11/09, Vit <vitruss at gmail.com> wrote: