Effect of Intra-atomic Correlation on London Dispersion Interactions: Use of Double-Perturbation Theory

A simple double-perturbation-theory method is outlined for the calculation of the first-order effects of intra-atomic electron correlation on the dipole polarizability at imaginary frequencies, and on the London coefficient for interactions between two-electron systems. Both single-parameter Slater and Hartree—Fock orbitals are used as zero-order wavefunctions. The static polarizability of helium and the London coefficient for helium—helium interactions found with the Hartree—Fock wavefunction are (in atomic units) 1.3346 and 1.382, respectively; accepted values are 1.384 and 1.47. The extensions of this method to larger systems, higher multipole interactions, and more complicated zero-order wavefunctions are discussed.