[DFTB-Plus-User] How to effect a non-scc dftb calculation, it the current SK parameter compatible ?

Bálint Aradi aradi at uni-bremen.de
Fri Mar 24 03:39:24 CET 2017

Dear Peter,

> I would like to carry out a non-scc dftb calculation. But i have one 
> part not clear and need your advice. Say for example, the gold case.
> The SK parameter for gold in auorg folder is Au-Au.skf. Do i just
> simply set the SCC=no option  in the  script for my non-scc
> calculation? One part to pay attention to is that the repulsive
> energy in Au-Au.skf is fitted by assuming "band structure" and
> "charge fluctuation energy" existed and both terms are subtracted
> with respect to DFT energy during the fitting process of the
> repulsive energy. If now i just turn off " charge fluctuation energy
> " by setting "SCC=no", will the repulsive energy i use in Au-Au.skf
> not compatible to my non-scc calculation ? Shouldn't it be more
> reasonable to have a separate repulsive energy profile for the 
> non-scc case ? Does the admin have this non-scc repulsive energy
> profile that i can request from ?  Thank for your suggestions!

You are correct, if you set SCC=no, the repulsives in the Auorg set
(which where made with SCC = Yes) will not be correct. But depending on
the amount of charge transfer between the atoms in your system, you may
still get qualitatively correct forces this way, so you could prerelax
structures in non-scc mode and refine them with scc at the end. (This is
mostly what non-scc is used for.)

We usually do not bother to create a non-scc repulsive, as it is not
really useful. Either your system has not much charge transfer (e.g. a
slightly distorted Au supercell), then scc and non-scc repulsives would
be very similar. Or your system has a substantial charge transfer (e.g.
some defect in gold, or some molecule containing one Au atom), but then
making a non-scc calculation would give a wrong Hamiltonian (one not
considering this charge transfer), so fitting a repulsive with that
unphysical non-scc Hamiltonain would yield a non-physical and therefore
non-transferable repulsive.

Best regards,


Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen

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