CCL: Becke Johnson correction on vibrational mode intensities, e.g. Si6



 Sent to CCL by: "Stefan  Grimme" [grimme=-=thch.uni-bonn.de]
 Hi,
 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.
 Best
 Stefan