The Importance of Atomic and Molecular Correlation on the Bonding in Transition Metal Compounds

Abstract

An accurate determination of the separation between the low-lying atomic states (3dn 4s1. 3dn− 1 4s1. and 3dn− 2) of the trantion metal alomst required both extensive basis sets and a high level correlation treatment. Since molecular systems containing transition metal atoms often involve admixtures of atomic states. molecular calculation also must be designed to correctly incorporate the dominani atomic correlation effects. Jn addition, the large atomic exchange energy associated molecular calculatil also must be designed to correctly incorporate the dominan atomic correlation effects. In aodition. the larg atomic exchange energy associated with high spin coupled 3d orbitals requires that a balance between atomic exchange and molecular bonding effects be achieved. These two requirements often necessitate the use of an MCSCF reference wavefunction followed by extensive Cl calculations to provide an accurate description of molecules containing transition metal atoms. Several examples will be given including the dipole moment of the 2Λ state of NiH, which is a sensitive measure of the mixture of 3d04s2 and 3d94s1 in the NiH wavefunction. the dissociation energy of the X2Π state of CuO, which is sensitive to the correct mixture of the 3d94s1 and 3d10 Cu+ atomic states, and the bonding in CrO, where an equivalent description of the relative energies associated with the Cr 3d-3d atomic exchange and the Cr-O bond is important. Some examples of these effects in transition metal dimers will also be given. and molecular bonding effects he achieved. These two requirements often necessitate the use of an MCSCF reference wavefunction followed by extensive cakulalions to provide an accurate description of molecules containing transition metal atoms. Several examples will be given including the dipole moment of the 2▵. state of NiH, which is a sensitive measure of the mixture of :3d94s2 alld 3d94s1 in the NiH wavefunction. the dissociation energy of the X2Π state of CuO, which is sensitive to the correct mixture of the 3d94s1 and 3d10 Cu+ atomic states, and the bonding in CrO. where all equivalent description of the relative energies associated with the Cr 3d-3d atomic exchange and the Cr-O bond is important. Some examples of these effects in transition metal dimers will also be given.