The APMO-MOLPRO interface: Highly correlated electronic structure calculations with the inclusion of quantum nuclear effects at Hartree Fock level

Abstract

A computational interface between the MOLPRO electronic structure package and the APMO [2] code is presented here. The APMO code is an implementation of the nuclear and electronic molecular orbital approach [3,4,5] in which electrons and light nuclei of molecular systems are described simultaneously with molecular orbitals at Hartree-Fock and second-order Möller-Pleset levels of theory. The APMO-MOLPRO interface extends the applicability of the APMO code by allowing to correlate the electronic structure part at higher levels of ab-initio theory and to describe the nuclear response to electronic correlation effects, through the electronic first-order reduced density matrix. Some applications are presented to illustrate possible advantages of this approach over standard electronic structure treatments.