Use of partial (and full) Löwdin integral approximations in molecular orbital calculations on HCN and FCN

Abstract

Tests and applications of the PLA and FLA integral approximation methods are made by calculating a wide range of molecular properties for HCN using a basis of single-zeta atomic orbitals. A comparison of the results with those obtained from an ab initio calculation establishes the PLA method as the better of the two approximation methods. The molecular orbitals for HCN and FCN are then determined for five different X-C separations (using a double-zeta basis set), and the changes in the electron distribution of each molecule are discussed with the aid of appropriate electron density maps, as well as population analyses related to a basis of natural hybrids.