# In which irreducible representations shall I put the electrons in an F atom in PySCF?

I’m looking to complete ROHF energy calculations in PySCF for the F atom.

I need to update the irrep_nelec dictionary for F.
I know that the one for the O atom is:

O
irrep_nelec={'A1g': (2,2), 'E1ux': (1,0), 'E1uy': (1,0),'A1u': (1,1)})


If I don’t include the appropriate one for F, I encounter the following error:

output file: out.txt
<class 'pyscf.scf.rohf.ROHF'> does not have attributes  irrep_nelec


I attempted to use pyscf to provide the correct dictionary:

import pyscf as pyscf
from pyscf import scf, gto

mol = gto.M(atom='F', basis='ccpvdz', symmetry=True, charge=0, spin=1, verbose=0)
mf = scf.RHF(mol)
mf.scf()
print(mf.get_irrep_nelec())


to yield the following output: {'s+0': (2, 2), 'p-1': (1, 1), 'p+0': (1, 0), 'p+1': (1, 1), 'd-2': (0, 0), 'd-1': (0, 0), 'd+0': (0, 0), 'd+1': (0, 0), 'd+2': (0, 0)}

I can compare to O,  {'s+0': (2, 2), 'p-1': (1, 1), 'p+0': (1, 0), 'p+1': (1, 0), 'd-2': (0, 0), 'd-1': (0, 0), 'd+0': (0, 0), 'd+1': (0, 0), 'd+2': (0, 0)} however this does not enable me to uniquely identify the correct dictionary.

• You need to include your full input and output files for all questions: mattermodeling.meta.stackexchange.com/q/417/5. Commented Apr 12 at 12:35
• Is it possible to just use the dictionaries returned by PySCF? Or can you not use the spherically symmetric point group for some reason?
– Tyberius
Commented Apr 12 at 20:24
• @Tyberius, I did attempt to do so, however the output was far from what I expected. Commented Apr 13 at 13:53
• @Ihavenofreetimeanymore, understood. I’ll follow the model set out by the examples. Commented Apr 13 at 13:54
• @TheorVHP I'm not sure how many times I'm going to need to say this, but you need to include all of your output files. Saying "the output was far from what I expected" is very unhelpful, and just suggests that "what you expected" is far from the science that the PySCF authors know. Commented Apr 15 at 5:03

{'A1g': (2,2), 'E1ux': (1,0), 'E1uy': (1,0),'A1u': (1,1)}

Then for fluorine I would simply put one more electron in either of E1ux or E1uy.