Vibration Data To Molden

Hello. I am using psi4 in psithon mode. I would like to write normal mode data to Molden, but having some difficulty.

set normal_modes_write on

The above does not work and I have tried many different syntax. Should I expect two molden files, one for wfn, and one for normal modes? Can anyone help?

Also, can psi4 output calculated bond lengths after optimisation, or do I need to calculate them from the resulting cartesian coordinates?

Many thanks.

The frequencies is just an order of events problem. The molden file for vibrations is written at the end of the frequency call, so you need to set normal_modes_write before the frequency call. The resulting molden file has information about normal modes, and nothing else.

As for “output calculated bond lengths”, it isn’t clear to me what you’re asking for. Looking at the output file tells you that Psi prints information about the bond lengths used as optimization coordinates over the course of the optimization. If you’re asking for a convenient Python way to access these, I believe the only way is to compute them yourself from the molecular geometry.