Incomplete orbitals-new elements in ionic bonding

Resonances, as opposed to true states, need not contain a full complement of electrons. Thus an anion may have a filled resonant p state well below the Fermi energy with less than six electrons. This mechanism of decharging alleviates electrostatic problems at surfaces and in multivalent ionic compounds. An unavoidable consequence of incompleteness is that the anion behaves as a repulsive scatter at electron energies above the resonance. The authors introduce the concept of a complementary resonance induced by the anion on the cation and which forms part of the valence band in an ionic compound.