Charge, spin and theoretical densities in transition metal complexes

Abstract

The results of diffraction experiments, of X-rays to give charge density and of polarised neutrons to give spin density, are compared between themselves and with the theoretical density obtained by a local density unrestricted Hartree-Fock calculation. The systems studied include in particular the archetypal M(CN)63− and M(OH2)62+ ions. Electron-electron correlation effects on their distribution can be as large as covalent bonding transfers, so there may be no simple relationship between the charge and the spin densities. Covalence appears to be appreciable even for the most ionic of crystals, but its effects are often masked by the correlation terms. The local density calculations can give a good account of the densities and of spectra in complexes in which the ground state is not orbitally degenerate. Orbital degeneracy emphasises the correlation problem and theory beyond the UHF treatment will be required.