Photoionization of Lithium by the Method of Polarized Orbitals

The method of polarized orbitals is used to calculate the photoionization cross section of lithium for photon energies from threshold to 15 eV. Initial-state corrections are obtained by representing the lithium atom as a perturbed Li⁺ core plus an electron in the $2s$ state. Final-state corrections are similarly obtained by including perturbations of the Li⁺ core by the continuum electron. Results are obtained using the length and velocity forms of the matrix elements, and are in good agreement with one another as well as with existing calculations using many-body perturbation theory. The theoretical results compare favorably with experimental data near threshold, but disagree slightly for higher energies.