Electronic structure and bonding of the ground state of alkaline-earth-metal monoxides and carbides

The electronic structure of the ground state of monoxides MO and carbides MC2 with M an alkaline-earth-metal atom (Be to Ba) has been investigated. Bond energies, vibrational frequencies, dipole moments and equilibrium bond lengths have been calculated using a hybrid density functional method. To understand the bonding characteristics, the ELF (electron localization function) and the NBO (natural bond orbitals) have been used. It has been found that despite many similarities between the monoxides and the carbides there is a difference in the bond formation. The results suggest that in the monoxides, and not in the carbides, a change in the type of bonding occurrs in going from the beryllium compound to the barium compound. For the carbides, all of them present an ionic bonding with a most favorable bent structure.