The polarized frozen-core approximation: A variational derivation of the alphabetic potential

The adiabatic polarisation potential experienced by a single valence electron in the field of an N-electron atomic core is derived variationally from the polarised orbitals of the core electrons. The resulting valence electron energies are in excellent agreement with observed ionisation energies of a large number of levels of the ions Si IV, P V and S VI, and electric dipole oscillator strengths computed with the valence orbital wavefunctions and energies are expected to be highly accurate.