Distinguishable-electron method for electronic structure calculations. IV. Polarizability of three- and four-electron atoms

The distinguishable electron perturbation method is applied to the polarizability of three- and four-electron atoms, with results comparable to much more complicated coupled Hartree-Fock calculations. For the initial approximation we use a product of Slater-type orbitals with exponents optimized via the Rayleigh-Ritz principle. Using accessible correlation expressions the polarizability can be computed to first order in correlation without resorting to correlated wavefunctions. The polarization functions required for this calculation are found exactly as solutions of one-electron perturbation equations. We introduce adjustable parameters into these equations which do not affect the energy but are optimized with respect to the polarizability property.