Application of the many-body Green's function formalism to the lithium atom

The techniques of many-body Green's function theory have been applied to the calculation of properties of the lithium atom. Using basis set expansion techniques and a second-order expansion of the self-energy, Dyson's equation was solved, and the first-order reduced density matrix and the first ionization potential for the lithium ground state were computed. The natural spin orbitals of s symmetry were in excellent argeement with those computed from wavefunctions. The ionization potential was within 0.01 eV of the exact experimental result.