Gaussian 03 Online Manual
This method keyword requests a Hartree-Fock calculation. Unless explicitly specified, RHF is used for singlets and UHF for higher multiplicities. In the latter case, separate α and β orbitals will be computed [57,58,59]. RHF, ROHF or UHF can also be specified explicitly.
SCF single point energy calculations involving basis sets which include diffuse functions should use the SCF=Tight keyword to request tight SCF convergence criteria.
Energies, analytic gradients, and analytic frequencies for RHF and UHF and numerical frequencies for ROHF.
The Hartree-Fock energy appears in the output as follows:
SCF Done: E(RHF) = -74.9646569691 A.U. after 4 cycles Convg = .6164D-03 -V/T = 2.0063 S**2 = .0000
The second and third lines give the SCF convergence limit and the expectation value of S2.