Manyhyphen;body theory of exchange effects in intermolecular interactions. Density matrix approach and applications to Hendash;Fminus;, Hendash;HF, H2ndash;HF, and Arndash;H2dimers

摘要

The firsthyphen;order exchange energy for the interactions of closedhyphen;shell manyhyphen;electron systems is expanded as a perturbation series with respect to the Moslash;llerndash;Plesset correlation potentials of the monomers. Explicit orbital formulas for the leading perturbation corrections are derived applying a suitable density matrix formalism. The numerical results obtained using the Moslash;llerndash;Plesset perturbation expansion, as well as nonperturbative, coupledhyphen;cluster type procedure, are presented for the interactions of Hendash;Fminus;, Hendash;HF, H2ndash;HF, and Arndash;H2. It is shown that the correlation part of the firsthyphen;order exchange energy increases the uncorrelated results by 10percnt; to 30percnt; for the investigated range of configurations. The analysis of the total interaction energies for selected geometries of these systems shows that at the present level of theory the symmetryhyphen;adapted perturbation approach correctly accounts for major intramonomer correlation effects and is capable to accurately reproduce the empirical potential energy surfaces.