Hi,

I am looking for a way to restart a SCF calculation from a reference wavefunction, without the file 180 (or maybe I need to generate a 180 file with my scf_wfn but I don’t know how to proceed).

Context: I first do a scf calculation like

```
psi4.core.set_output_file(molecule.filename + ".out", False)
psi4.set_options({'basis': 'STO-3G',
'reference': 'rfh',
'e_convergence': '12',
'scf_type': 'direct',
'puream':False})
scf_e, scf_wfn = psi4.energy('scf', return_wfn=True)
```

Then, I transform the MO coefficient matrices and I set them back to the wavefunction objet as follows:

```
scf_wfn.Ca().np[:] = alpha_new_coeff
scf_wfn.epsilon_a().np[:] = alpha_new_energies
```

Similarly for beta if needed.

Finally, I tried

```
psi4.energy('scf', ref_wfn=scf_wfn)
```

but I got the following error:

```
ValidationError("Cannot seed an SCF calculation with a reference wavefunction ('ref_wfn' kwarg).")
```

Why cannot we seed a SCF calculation with a reference SCF wavefunction, if the basis is the same but only coefficients are different ? It can be useful to check that the transformation of the occupied orbitals span the same space as the canonical ones, among other things.

Otherwise, how can I bypass this issue ? Can I create a 180 file with my new scf_wfn object and set “guess read” ? If yes, how should I proceed?

Thank you