A-SAPT calculations / analysis


I am new to the PSI4 and maybe I have overlooked something.

I would like to perform atomic A-SAPT calculations and depict their results as it was nicely done in one of your papers: R. M. Parrish and C.D. Sherrill, J. Chem. Phys. 141, 044115 (2014).

Is it possible to do with current PSI4 code?
Where to start?

Thanks in advance,

There is an updated version of A-SAPT called functional group SAPT (F-SAPT) available in PSI4. The manual page for this method is available here. You can find references to the papers related to F-SAPT (including the one you linked) in the second paragraph.


Thank you for your reply,

Yes, I know about F-SAPT, but I am particularly interested in estimating atomic effects on my solute molecule.

Unfortunately, I investigate aromatic system so, at least as far as I tried, I cannot use F-SAPT for getting insight into inter-atomic effects. I know there are some doubts on how to divide some effects between the atoms, but still, it would be great if I could find a way to extract this information from PSI4, if possible.

I think you want to perform an I-SAPT calculation instead of F-SAPT. This allows you to obtain the SAPT0 interaction energy between two noncovalent fragments A and B that are each covalently bonded to a linking fragment C. I think you can define the fragments A and B such that they each contain one atom and define the fragment C as the rest of the molecule. This should work as long as the atoms in A and B do not directly share a covalent bond.

Thanks !

I will give it a try this way, then.

@michal you are exactly correct that you should be wary of breaking aromatic bonds within F-SAPT. Unfortunately, A-SAPT isn’t currently available within the public release of Psi4 – our apologies. This may change in the future, but for the moment I would like to caution you with respect to utilizing atomic fragments within F-/ISAPT.

As a general rule, I recommend strongly against using atomic fragments in either the F-SAPT or ISAPT partitioning schemes. The reason for this is that atomic fragments can be dicey at best within the F-SAPT post-analysis phase of the computations (i.e., running fsapt.py within your fsapt/ directory); the charge assignment for link bonds between atomic fragments (either by charge or 50-50) can

  • yield drastically different results between link assignment scheme, and
  • both kinds of link assignments can lead to spurious dipoles on atomic fragments,

either of which can influence the overall F-SAPT analysis in unexpected ways. However, since utilizing atomic fragments seems to be your only current way forward, just be very careful to check that your results make chemical sense. Also, be sure to thoroughly check the Orbital Check section of the fsapt/frag_A.dat and fsapt/frag_B.dat files, as values more than 0.05-0.1 electrons lost from doubly occupied orbitals in a fragment can indicate that the F-SAPT analysis of a particular fragmentation scheme may no longer be valid.