[Pw_forum] Graphene--Silicon Surface(scf not converge)

[Giovanni Cantele]

> Hi everyone:
> I am doing a scf calculation for my structure. My structure has 660
> atoms(56 H,324C,280 Si). I use H terminated Si-C surface. But after 24
> hours calculation(46 steps), the scf accuracy still fluctuate from about 1
> to 100.
> Does anyone ever know this before?How to solve it?
> Thank you very much!

You can try to:
1) browse the forum, the issue has been discussed many many times, there
is not a unique answer the problem might be related to several issues

2) browse the QE wiki:
http://www.quantum-espresso.org/wiki/index.php/Frequently_Asked_Questions#Self-consistency_is_slow_or_does_not_converge_at_all

Did you check your geometry using, e.g., XCrysDen? Some times, mostly when
dealing with such a huge number of atoms, a wrong coordinate might give
atom overlap preventing the scf cycle from converging. You might also try
to tune some parameters related to the convergence of the scf cycle, like
mixing_beta.

Giovanni

-- 
Dr. Giovanni Cantele
CNR-SPIN and Dipartimento di Scienze Fisiche
Universita' di Napoli "Federico II"
Complesso Universitario di Monte S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
Phone: +39 081 676910 - Fax:   +39 081 676346
ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele
Research Group: http://www.nanomat.unina.it
Skype contact: giocan74