The electronic structure of an ionic crystal is investigated with the assumption that the solutions of Fock's equations for the valence electrons can be expressed as linear combinations of the outer orbitals on the negative ions and the first vacant orbitals on the metal ions. The inclusion of this latter group of orbitals allows for homopolar binding. Numerical calculations are made for LiF and the width of the F-2p band is found to be 5.4 ev of which about 5% is due to homopolar binding. The main homopolar effect is to provide a coupling between ions which are second nearest neighbours in the halide ion lattice.