[DFTB-Plus-User] E(rep) question

[Bálint Aradi]

Dear Tom

> three parts - a close in exponential fit, a cubic spline
> in the "bonding" part, and zero after a cutoff value -
> these parameters being specified in the .SKF files.
> 
> I gather from some papers that the close-in part is a 3-parameter 
> exponential. From the code, it appears to be y = exp(-ar+b)+c
> Is this so?

 Indeed, we are using that expression to model the very short range
interaction. However, you should be aware of the fact, that the
exponential in this region (usually distances below 0.5 A) is rather a
way to make sure the atoms do not do anything unphysical if for some
reasons (high temperature, or simulation of ion bombardement with high
speed) they approach each other too much, as an accurate description of
the physics happening at that range.


  Best regards,

    Bálint


Ps. I CCd my response to the DFTB-Plus-User list. Please post your
questions to this list rather then sending it to me, so that other also
can profit from your questions/experiences.

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/en/~b_aradi


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