SUM-RULE FOR A METALLIC INTERFACE

A sum rule for the electronic scattering amplitude has been derived fo r a metallic interface. The result is a generalization of that given p reviously for a metal surface. The sum rule that provides a general re lation between the scattering amplitude and the bulk characters of the metals should prove useful in a variety of calculations of metallic i nterface properties. In addition, a connection condition that can be u sed to define an intrinsic scattering matrix is proposed.