On the accuracy of the algebraic approximation in molecular electronic structure calculations: VIII. Matrix Hartree-Fock and many-body perturbation theory applied to a negative molecular ion

摘要

A previously reported study of the CN- anion at the matrix Hartree-Fock level failed to match the accuracy achieved in studies of isoelectronic neutral diatomic systems. In this paper, we examine the CN- ion again at both the Hartree-Fock level and including the effects of electron correlation by means of finite-order many-body perturbation theory. A basis set which supports a matrix Hartree-Fock energy 2.0 μHartree above the corresponding finite difference energy is constructed. Over 98.5% of an estimate of the exact second-order correlation energy component is recovered by a basis set containing atom-centred and bond-centred functions of s, p, d, f, g and h symmetry. The calculated energies are compared with those supported by other published basis sets.