Molcas Forum

Xcy

Member

Registered: 2017-11-20

Posts: 3

How to get gradients and derivative coupling vectors for any CI

Hello Molcas developer,

I'd like to get the topography of potential energy surface of Conical Intersection seam. The gradients and derivative coupling vectors are printed after a converged Conical Intersection optimization but is there a way to obtain those vectors for any CI structure? Like a CI reached by a trajectory instead of converged CI? Thank you.

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,201

Re: How to get gradients and derivative coupling vectors for any CI

If you already have the structure of your CI, you could try a CI optimization from there setting very large convergence thresholds in SLAPAF: the initial structure should be considered as converged and you'll get the CI characterization.

If you don't have the structure, you should first try to get a structure where you have the energy degeneracy such that the analysis is valid. An imaginative combination of different constraints, in particular "sphere" should help you find a meaningful crossing point.

For any structure you can always compute gradients and/or nonadiabatic coupling with ALASKA (for the latter use NAC and NoCSF keywords) and handle them manually.