A Green's function perturbation technique was presented which was appropriate for obtaining the change in the total electronic energy when the surface atoms of a crystal reconstruct in a periodic manner. The phase shift technique was used to determine the change in the density of states. The method was quite general and could be used to study arbitrary reconstructed surfaces. As an illustration, explicit equations appropriate to the (2 x 1) reconstruction of a square lattice were presented. Surface Reconstruction of a Two-Band Crystal I - Green's Function Formalism. S.L.Cunningham, W.Ho, W.H.Weinberg, L.Dobrzynski: Applications of Surface Science, 1977, 1[1], 33-43