MANY-BODY THEORY OF INTERMOLECULAR INDUCTION INTERACTIONS

The second-order induction energy in the symmetry-adapted perturbation theory is expressed in terms of electron densities and polarization p ropagators at zero frequency of the isolated monomers. This expression is used to derive many-body perturbation series with respect to the M oller-Plesset type correlation potentials of the monomers. Two expansi ons are introduced-one based on the standard Moller-Plesset expansion of electron densities and polarization propagators, and the second acc ounting for the so-called response or orbital relaxation effects, i.e. , for the perturbation induced modification of the monomer's Fock oper ators. Explicit orbital formulas for the leading perturbation correcti ons that correctly account for the response effects are derived throug h the second order in the correlation potential. Numerical results are presented for several representative van der Waals complexes-a rare g as atom and an ion Ar-Na+, Ar-Cl-, and He-F-; a polar molecule and an ion H2O-Na+ and H2O-Cl-; two polar molecules (H2O)2; and a rare gas at om and a polar molecule Ar-HCl and He-HCl. It is shown that in the abo ve systems, the significance of the correlation part of the induction energy varies from a very important one in the complexes of rare gas a toms and ions to a practically negligible one in the complexes of rare gases with polar molecules.