The origins of the similarities between late transition metals and early transition metal monocarbides

Abstract

Full potential electronic structure calculations have been conducted on transition metal mono-carbides of the NaCl and WC structure. These calculations reveal that carbon p-orbitals hybridize strongly with some, though not all, of the metal d-orbitals. These strongly hybridized orbitals give rise to covalent bonds, with an occupied region which is p-d bonding, within the unit cell, separated by an energy gap from an unoccupied region which is p-d antibonding within the unit cell. The remaining unhybridized metal orbitals fill this gap, forming a band that can best be described as metallic in character. The same type of metallic band is seen to be coincident with the Fermi energy of the Group 8–10 transition metals. As a result, for the correct number of pd electrons, the Fermi energy of the monocarbides passes through a region of metallic bonding, giving rise to metallic properties and catalytic behavior similar to the Group 8–10 metals.