Comparative study of errors in HeH? interaction energy calculations

Abstract

Basis set truncation error BSTE , size extensivity Error SEE , zero point Ž . Ž . y vibrational energy ZPVE , and basis set superposition error BSSE of HeH weak van der Waals interaction energy were determined and compared at the self-consistent field Ž . Ž . Ž . SCF , many-body perturbation theory MBPT , and coupled cluster CC methods using even-tempered functions. Isotope substitution effects and the role of bond function Ž . augmentation were taken into account. Apart from core correlation energy error CCEE , which is absent from HeH y interaction energy, the results confirm that BSTE is the most Ž . important source of error, followed by SEE of the truncated configuration interaction CI expansion, ZPVE and BSSE in a descending order. Introducing quadrable excitations to the truncated CI expansion reduces the magnitude of SEE by ; 45.7%, and BSSE correction is not necessary even at the electron correlation level. While bond function augmentation reduces BSSE at the Hartree᎐Fock, it has an oscillating behavior at the electron correlation level.