Ab initio study of electronic properties in free and matrix-isolated iron dihalides

Ab initio Hartree-Fock calculations are performed in the molecular g5, g5, and g+5 states of the dihalides FeCl2 and FeBr2 at experimental and geometry-optimized atomic separations. Molecular-term energies, ionization energies, bond energies, electric-field gradients (EFG), and electron densities (o) (the latter two quantities at the iron nucleus) are evaluated and compared with experiment. Electron-correlation corrections and basis-set effects on the energies, EFG, and (0) are studied. The relative isomer shift of noble-gas-matrix-isolated FeCl2 and Fe0 is analyzed on the basis of electron densities calculated in FeCl2noble-gas and Fe0noble-gas clusters.