[DFTB-Plus-User] Fwd: SCC convergence problem for cluster calculation

[Bálint Aradi]

Dear Anjali,

  Apart of some special cases, DFTB+ shows usually a nice SCC
convergence behaviour. Are you sure, that your input is physically
meaningful? Especially, that atoms are not unphysically close to each other?

 One thing I note in your input, that your Broyden-mixing parameter is
extremely low. Usually, 0.1-0.2 is the right range. Also, you could as
suggested by Rodrigo already, set SCCTolerance less tight as the default
value (e.g. set it to 1e-4 instead of the default 1e-5).

  Alternatively, if you geometry is rather unphysical, you could set
ConvergentForcesOnly = No in the ConjugateGradient section. This would
allow for relaxation along non-convergent forces as long as your system
does not become more physical. Similarly, you could just set SCC=No for
a while, relax the sytem, and restart then with SCC = Yes.

 I hope, some of the ideas will help you.

  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: signature.asc
Type: application/pgp-signature
Size: 259 bytes
Desc: OpenPGP digital signature
URL: <http://www.dftb-plus.info/pipermail/dftb-plus-user/attachments/20121017/12a2bd9e/attachment.pgp>