From: Daniel Fellner (
Date: Wed Apr 13 2022 - 12:33:04 CDT

It's me again,

During some angle optimisation, I noticed two angles terminating in
carbonyl carbon were converging to unbelievably low force constants.
Testing these parameters in MM minimisation shows these angles deviate from
QM even more than the original parameters.

I believe the issue is favourable 1,6 interactions between the carbonyl
oxygen and a phenyl hydrogen nearby, contaminating the resulting PES.
What's the best course of action? Exclude these angles from optimisation?
Recalculate the Hessian at a geometry lacking these interactions?
Iteratively fit these guided by IR? Or is there some way to decouple the
interaction during optimisation/Hessian calculation?

Kind regards,

*Daniel Fellner BSc(Hons)*
PhD Candidate
School of Chemical Sciences
University of Auckland
Ph +64211605326