An effective core potential investigation of Ni, Pd, and Pt and their monohydrides

摘要

The nickel, palladium, and platinum atoms and their monohydrides are investigated using effective core potentials (ECPrsquo;s) recently introduced by Hay and Wadt lsqb;J. Chem. Phys.82, 270, 299 (1985)rsqb;. The palladium and platinum ECPrsquo;s include relativistic effects. Two types of ECPrsquo;s, which differ in their definition of the core region, are used in conjunction with large valence basis sets including thinsp;fthinsp; functions. Electron correlation is incorporated by Moslash;llerndash;Plesset perturbation theory through fourth order. The results demonstrate the success of the ECP approximation: they are similar in quality to those of allhyphen;electron studies and at the same time are achieved at a reduced computational cost. Total correlation energies obtained with both types of ECPrsquo;s are compared, and are found to be very sensitive to details of the basis set. Correlation effects are treated more consistently by the ECPrsquo;s which include the outermost core orbitals in the valence region. The relative ordering of molecular states is calculated to be2Dgr;2Pgr;ap;2Sgr;+for NiH,2Sgr;+2Dgr;2Pgr; for PdH, and2Dgr;ap;2Sgr;+2Pgr; for PtH. Trends in bond lengths and bond strengths in the nickel, palladium, and platinum series are discussed.