The problem is not that we are missing a check, but that the error message we already have isn’t firing. When I try to run water cation as an RHF system, I get an error message like you requested.
molecule {
1 2
O
H 1 1.0
H 1 1.0 2 104.5
}
set reference rhf
energy('scf/sto-6g')
!----------------------------------------------------------------------------------!
! !
! Fatal Error: RHF: RHF reference is only for singlets. !
! Error occurred in file: !
! /Users/jonathonmisiewicz/psi4/psi4/src/psi4/libscf_solver/rhf.cc on line: 92 !
! The most recent 5 function calls were: !
! !
!----------------------------------------------------------------------------------!
As Holger said, we need more information. Steps 4 and 5 of our guidance for posting help topics are not optional. In addition to what Holger requested, I need to know how you ran your input. I’ve seen one error message about PyCapsule before, and that was a problem specific to when Psi was running in a Jupyter notebook.