We considered a muffin-tin periodic potential (-δ inside the spheres and zero outside). Using the augmented-plane-wave method we studied systematically the location of gaps for positive energy and for various values of δ and the sphere radius a. Our results are applicable to the problem of classical wave propagation in composite media and relevant to the problem of optical localization.

• Received 30 March 1989

DOI:https://doi.org/10.1103/PhysRevB.40.1334