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

Abstract

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.

Comparison of the polarizabilities and hyperpolarizabilities obtained from finite basis set and finite difference Hartree–Fock calculations for diatomic molecules: III. The ground states of N2, CO and BF

“…The results are compared with finite basis set calculations of the corresponding quantities which are carried out analytically using coupled perturbed Hartree-Fock theory. The basis sets developed in our previous studies [66,67] have also been used in the construction of basis set suitable for electron correlation studies [79][80][81]. It is anticipated that the basis sets developed in the present work will provide a starting point for studies of molecular polarizabilities and hyperpolarizabilities which take account of electron correlation effects.…”