Convergency of some properties of electrostatically interacting molecules from accurate CI multipole function calculations

Abstract

The electric multipole moments up to the hexadecapole, as well as their first and second derivatives with respect to internuclear distance, have been calculated from near Hartree-Fock wavefunctions supplemented by medium size CI treatments. For HF the octupolar and hexadecapolar moments are respectively Ω _zzz = 1·699 DŲ, Φ _zzzz = 1·804 Dų, while for HCl Ω _zzz = 2·446 DŲ and Φ _zzzz = 4·704 Dų. Lower moments are in agreement with experimental values.

The convergency of two expansions of the electrostatic potential, that differ in the way they are quenched, as well as the corresponding geometries is then discussed. It is concluded that the expansion should be exponent truncated (ET) rather than moment truncated (MT).