I found that INTDER program developed by Prof. W. Allen and co-workers is capable of doing vibrational analysis in terms of internal coordinates. It seems to be a part of Psi2 and Psi3 package, but, I am not sure if it is available in the current version as well. I tried searching the manual, but couldn’t find anything on it. If anyone can tell me the way to use INTDER with Psi4, I would be grateful.
Colleagues, any update on this question? I am also interested
INTDER and INTDIF (I can never remember which is which) currently exist as scripts used by Prof. Allen and students working with him. He hasn’t been associated with Psi in years. You’ll need to contact him for the script.
INTDER isn’t the easiest code to use and Psi4 currently doesn’t generate all the data files that it would need. I have several grad students that have been using it recently. I’ll see if I can get one of them to work on an interface.