CCL: Becke Johnson correction on vibrational mode intensities, e.g. Si6
- From: "Stefan Grimme" <grimme a
- Subject: CCL: Becke Johnson correction on vibrational mode
intensities, e.g. Si6
- Date: Fri, 24 Mar 2017 04:37:34 -0400
Sent to CCL by: "Stefan Grimme" [grimme=-=thch.uni-bonn.de]
I can't say much about your actual calculations but want to clarify
this issue. The dispersion energy with BJ-damping becomes constant
at short interatomic distances meaning that the forces vanish.
This is more physical than the previously used zero-damping which introduces
artificial repulsive dispersion forces a short distances. When the
forces vanish there can not be a contribution to the force constant
(i.e. vibrational frequencies). Because in Si6 dispersion corrections
are anyway small (its a small molecule), your observation seems to me the result
of a bug in the code rather than a physical effect.