Improvement of STO and GTO Basis Set Quality in Calculations of Magnetic Properties by the Coupled and Uncoupled Hartree−Fock Perturbation Theory

Abstract

Two methods of physically justified improvement of the STO and GTO basis set quality are suggested for ab initio calculations of molecular magnetic properties. They are based on the analysis of analytical expressions for the first-order correction (response) functions to the unperturbed basis AO's. The response functions have been obtained by solution of the inhomogeneous Schrodinger equation for the model problem “a one-electron atom in an external uniform field”, by the closed representation of the Green's function. It has been shown that unlike the London orbitals for magnetic field the Green's function method enables us to get the general solutions of the inhomogeneous Schrodinger equation. The methods elaborated have been applied in test calculations of magnetic susceptibilities and nuclear shielding constants of the first- and second-row hydrides and diatomics in STO-NG, split-valence CGTO basis sets, and extended ones constructed on their base. Analysis of results obtained has allowed us to determi...