Request to implement selective unharmonic treatment in VPT2

[tapacikk]

Hello,

I wanted to thank you for your code (I luv Psience!) , it has been really helpful in my research. I would like to request a new feature for the code that would allow for anharmonic treatment of select vibrational modes. The molecules that I study are quite large and it is not possible to obtain the full set of 3n-6 modes.

In Gaussian, there is an option called "SelectAnharmonicModes" which allows for the treatment of only select vibrational modes in an anharmonic way. This means that potential expansions in the .fchk file are only available for selected modes. However, as far as I understand, your code expects the modes and their potential expansions for the full set of 3n-6 modes. This means that there is currently no space for using "SelectAnharmonicModes" with your code.

One way to work around this would be to manually obtain expansions from the .fchk files and input them into the model via the parameters of your code while setting the third and fourth derivatives to zero for harmonically treated modes. However, it would be very helpful if your code could allow for a quick implementation of this feature.

Please let me know if there is already a way of doing what I have described or if you would like additional information.

Thank you.