Hi,
Cross-posted from Getting diagonal correction of Born-Oppenheimer approximation from PSI3
I saw https://onlinelibrary.wiley.com/doi/10.1002/jcc.20573
mentioned there is a diagonal Born-Oppenheimer correction (DBOC) in PSI3.
It seems in PSI4, DBOC is an interface to CFOUR
https://psicode.org/psi4manual/master/autodir_options_c/module__cfour.html
I hope DBOC will also be available in PSI4.