Nonrelativistic all electron SCF, MCSCF, and CI calculations on the AgH, AuH, and Ag2 molecules

Abstract

Near basis set limit SCF and proper dissociating MCSCF nonrelativistic potential curves are given for AgH, AuH, and Ag2. The importance of f functions in the Slater Ag basis, and low exponent f functions with the same spatial extent as the outer lobe of the Au 5d shell in the Slater Au basis, is demonstrated. Their inclusion adds ∼0.1 eV/heavy atom to dissociation energies and is absolutely necessary for determining basis set limit dipole moments. In CI calculations which correlate the bonding electrons and the outer d shells of the heavy atoms, the inclusion of f functions is shown to be even more important. For AgH, correlation effects are shown to decrease Re from a Hartree–Fock value of 1.774 to 1.702 Å (expt 1.618 Å), and to increase De from a Hartree–Fock value of 1.224 to 2.16 eV (expt 2.39 eV). Relativistic effects are responsible for the bond shortening not accounted for in these calculations. In AuH, remarkably parallel results are obtained. Correlation decreases the bond length from a Hartree–Fock value of 1.824 to 1.753 Å (expt 1.528 Å) and increases De from a Hartree–Fock value of 1.109 to 2.02 eV (expt 3.36 eV). The much larger remaining differences from experimental values reflect the much larger relativistic effects in gold containing molecules. Less complete calculations on Ag2 give a Hartree–Fock bond length of 2.791 Å and De=0.38 eV. Partial inclusion of bond and d-shell correlation effects shortens the bond length to 2.724 Å which is probably ∼0.08 Å longer than the true nonrelativistic value. A correlated De=1.13 eV (expt 1.67 eV) is computed, but this value is probably ∼0.4 eV too low because of limitations in basis set and correlation effects. Molecular quadrupole moments of all three molecules are discussed.