Herzberg-Teller couplings in FCON program

[TARAS KHVOROST]

Dear MOLPRO Team,

Thank you for your ongoing support! I am currently planning to calculate anharmonic Franck-Condon factors (FCFs) between two states using the FCON program. I have a specific question regarding the incorporation of Herzberg-Teller (HT) coupling, which arises from the geometry-dependent dipole moment, into these calculations.

Could you clarify whether the FCON program accounts for HT coupling directly? If not, do I need to construct the dipole surfaces using XSURF to effectively incorporate HT coupling effects, or is this aspect not considered at all in the current implementation?

I would appreciate any guidance you can provide on this matter to ensure accurate modeling of the phenomena in my calculations.

Kind regards,

Taras

[rauhut]

Dear Taras,

the HT terms have been implemented in principle (see JCP 152 (2020) 114109), but apparently the information about the transition dipole moments was implemented in some sort of quick hack and is neither described in the manual, nor is it conveniently supported by a set of keywords. Unfortunately, my co-worker, who implemented this part, left a couple of years ago and since then we did not follow the simulation of photoelectron spectra any longer.

Best,

   Guntram