[DFTB-Plus-User] Dear dftb+ developer, is a multipole expansion scheme available for the charge fluctuation term ?

[Bálint Aradi]

Dear Peter,

> Dear DFTB+ users and developers Recently, we have encountered some
> issues in calculating partial charge in small gold clusters. The
> charge we obtained seem to deviate systematically with respect to
> those calculated by DFT. I am wondering if a numerical scheme
> proposed in this paper ( Phys. Status. solidi B, No.2 ,259-269
> (2012)) is available, perhaps in the newest version of dftb+, or not
> ? I would like to learn whether adding higher order terms in addition
> to a mono-pole charge term can remedy the systematic deviance of
> partial charge predicted by dftb+ and DFT. Any suggestions or advice
> are much appreciated.Thanks.

Yes, we are working on the multipoles and hope to come up with a
reliably working within a few months. (First results are promising, but
a few peaces, like forces are still missing.)

As for the partial charges, you should be careful on comparing DFT and
DFTB charges. Depending on the charge partitioning scheme you use, you
would have different values. In DFTB+ (and in DFTB in general) we use
Mulliken-charges, which are, however, strongly basis dependent, so
comparing to DFT results could be tricky. One could try to plot total
charges on a grid and make Bader charge analysis for both DFT and DFTB,
that would be probably more comparable, as at least you would use the
same (basis-independent) charge partition scheme in both methods.

  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/


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