[DFTB-Plus-User] How to effect a non-scc dftb calculation, it the current SK parameter compatible ?
aradi at uni-bremen.de
Fri Mar 24 04:38:05 CET 2017
> Thank you for your kind reply. You have mention that the repulsive
> energy (RP) is fitted to bulk system of gold and since crystal gold
> will not have charge transfer or nearly zero charge transfer, the RP
> fitted will be similar to the non-scc case. However, in the case of
> gold clusters, there are in fact non zero charge transfer among
> atoms. And i believe the Rp in this case will be quite different to
> the bulk case since charge transfer now occurs in the former. In
> these two extreme cases ( bulk gold and gold clusters Au_n, where n
> is less than 10 ), do you think two separate RPs is necessary ?
> Because the Rp in Au-Au.skf is actually fitted to system with nearly
> zero charge transfer, yet in small clusters case, the charge transfer
> can't be neglected. I was speculating maybe the Rps will be quite
> different in these two cases. Would you provide any comments or
> advice ? Many thanks.
According to DFTB theory, the repulsive potential is only a functional
of the reference density, which is the superposition of the compressed
neutral atom densities. So the difference, between a system with
considerable charge transfer and a system with almost no charge transfer
must be described by the scc-part of the Hamiltonian, not by the
repulsive, as the reference density is similar in both cases. Therefore,
when done with care, it is usually possible to create repulsive
potentials, which are good compromises for both cases.
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
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