IMPROVEMENT OF STO AND GTO BASIS-SET QUALITY IN CALCULATIONS OF MAGNETIC-PROPERTIES BY THE COUPLED AND UNCOUPLED HARTREE-FOCK PERTURBATION-THEORY

Two methods of physically justified improvement of the STO and GTO bas is set quality are suggested for ab initio calculations of molecular m agnetic properties. They are based on the analysis of analytical expre ssions for the first-order correction (response) functions to the unpe rturbed basis AO's. The response functions have been obtained by solut ion of the inhomogeneous Schrodinger equation for the model problem '' a one-electron atom in an external uniform field'', by the closed repr esentation 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 equa tion. The methods elaborated have been applied in test calculations of magnetic susceptibilities and nuclear shielding constants of the firs t- 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 determine the field of applicabilit y for the suggested methods of basis set construction adapted for the magnetic properties calculations.