Floating point division by zero when running SAPT with H+ as a compound

[dspoel]

When using H+ as the compound in a SAPT calculation it crashes with a divide by zero error:

  File "/var/spool/slurm/d/job333055/slurm_script", line 21, in <module>
    myener = psi4.energy("sapt2+(ccd)dmp2")
  File "/home/spoel/miniconda3/lib/python3.8/site-packages/psi4/driver/driver.py", line 525, in energy
    wfn = procedures['energy'][lowername](lowername, molecule=molecule, **kwargs)
  File "/home/spoel/miniconda3/lib/python3.8/site-packages/psi4/driver/procrouting/proc.py", line 4581, in run_sapt
    monomerA_wfn = scf_helper('RHF', molecule=monomerA, **kwargs)
  File "/home/spoel/miniconda3/lib/python3.8/site-packages/psi4/driver/procrouting/proc.py", line 1887, in scf_helper
    e_scf = scf_wfn.compute_energy()
  File "/home/spoel/miniconda3/lib/python3.8/site-packages/psi4/driver/procrouting/scf_proc/scf_iterator.py", line 99, in scf_compute_energy
    scf_energy = self.finalize_energy()
  File "/home/spoel/miniconda3/lib/python3.8/site-packages/psi4/driver/procrouting/scf_proc/scf_iterator.py", line 692, in scf_finalize_energy
    self.print_energies()
  File "/home/spoel/miniconda3/lib/python3.8/site-packages/psi4/driver/procrouting/scf_proc/scf_iterator.py", line 804, in scf_print_energies
    self.set_variable("HF VIRIAL RATIO", - potential / ke)  # P::e SCF
ZeroDivisionError: float division by zero

The script to reproduce this is below.

#!/usr/bin/env python3
import os
import numpy as np
import psi4 as psi4
psi4.core.set_num_threads(4)
psi4.set_options({"cachelevel": 1, "print": 1})
psi4.set_memory(12000000000)
psi4_io = psi4.core.IOManager.shared_object()
psi4.core.set_output_file('hcl-sapt.log', False)
geometry= """
 1 1
 H -0.0 0.0 -1.36
 --
 -1 1
 Cl 0.0 0.0 1
"""
geom = psi4.geometry(geometry)
psi4.basis_helper("""
assign aug-cc-pvtz
""")
myener = psi4.energy("sapt2+(ccd)dmp2")
for ener in [ 'SAPT ELST ENERGY', 'SAPT EXCH ENERGY', 'SAPT IND ENERGY', 'SAPT DISP ENERGY', 'SAPT TOTAL ENERGY' ]:
    print("%s %g" % ( ener, psi4.variable(ener) ))

[JonathonMisiewicz]

Ah yes, you can't have an electron kinetic energy if you don't have electrons...

[dspoel]

That makes sense, but does that mean this cannot be fixed with an if statement? This is only printing after all.

[JonathonMisiewicz]

No, this isn't only printing. This is a Psi variable that can't be defined due to the exceptional circumstance of having zero electrons. I defer to @loriab for deciding what to do about this one.