Magnetic Hyperfine Structure of Lithium, Using an Approximate Projected Hartree-Fock Method

An approximate projected Hartree-Fock calculation is performed for the ²S ground state of the Li atom. It is shown that the use of general spin orbitals is essential for the treatment of the spin degeneracy in many-electron atoms. The energy obtained is -7.447536 a.u., which is lower than perviously published values obtained from s orbitals only. The value for the Fermi contact term is 2.846 a₀^-3, which is 97.9% of the experimental one. A natural spin-orbital analysis of the wave function is performed.