Relativistic and correlation effects in CuH, AgH, and AuH: Comparison of various relativistic methods

Abstract

The effects of relativity on the bond lengths, dissociation energies, and harmonic vibrational frequencies of the 1Σ+ electronic ground states of the group IB hydrides CuH, AgH, and AuH have been evaluated with a variety of ab initio methods. These properties were investigated with moderately-sized basis sets at the self-consistent field Hartree–Fock (SCF-HF) level and with second-order Mo/ller–Plesset (MP2) perturbation theory for electron correlation. Comparisons were made between all-electron results using the nonrelativistic Hamiltonian, perturbation theory (PT-MVD) at first-order with only the one-electron nonfine-structure terms of the Breit–Pauli Hamiltonian, the spin-free Douglas–Kroll (DK) transformed Dirac Hamiltonian and the untransformed Dirac Hamiltonian, and results using two sets of relativistic effective core potentials (RECPs). The expected trends of bond length decrease, dissociation energy increase, and harmonic vibrational frequency increase with both relativity and correlation are found. Both sets of RECPs are shown to give good results, if accompanied by a reasonable basis set. The DK method is demonstrated to be an inexpensive, reliable approximation to the DHF method.