Polarized basis sets for high-level-correlated calculations of molecular electric properties

Summary

The first-order polarized basis sets PolMe are generated for elements (Me=Cu, Ag, Au) of group Ib of the periodic table by using the basis set polarization method developed in earlier papers. The performance of these basis sets is extensively tested in calculations of atomic dipole polarizabilities with particular attention given to the evaluation of the electron correlation and relativistic contributions. The extension by theg-type polarization functions (PolMe-g sets) is devised for use in accurate calculations of atomic and molecular electric properties. The (negative) electron correlation contribution to dipole polarizabilities of all elements of group Ib, as calculated at the level of the spin adapted coupled cluster method with single and double excitations and non-iterative corrections for the contribution of the T₃ clusters (SA CCSD(T)), remains at the same level relative to the ROHF data. The pure relativistic correction to the ROHF results, evaluated within the quasirelativistic approximation involving the mass-velocity and Darwin corrections, is negative and rapidly increases with increase of the nuclear charge. Its large negative value is, for heavier systems, partly compensated by a positive contribution from the mixed relativistic-correlation terms. Our relativistically corrected SA CCSD(T) calculations predict the following values of the dipole polarizability in the coinage metal series: 46, 51, and 29 a.u., for Cu, Ag, and Au. The present results for Cu and Ag agree well with recent pseudopotential calculations by Schwerdtfeger and Bowmaker. However, for Au our result is by about 6 a.u. lower than that obtained by using 19-electron relativistic potentials. Several possible reasons for this discrepancy are discussed. The PolMe and PolMe-g basis sets are also used to calculate electric dipole polarizabilities of the singly positive ions of group Ib elements. The results obtained in the quasirelativistic CCSD(T) approximation are 6.6, 9.2, and 11.8 a.u. for Cu⁺, Ag⁺, and Au⁺, respectively. These values follow the pattern expected for the series of ions whose polarizability is dominated by the next-to-valenced shell.