Eliminating poles in the KKR determinant in band-structure calculations

The determinant of the secular equation for calculating the band structure by the method due to Korringa, Kohn, and Rostoker (KKR) has poles at $E= |k+G_n|^2$, where $G_n$ are the reciprocal-lattice vectors. It is shown that one can obtain an equation having a matrix whose elements and determinant are continuous functions of the energy over a particular range. This eliminates the difficulties in calculating the spectrum near the poles and enables one to alternate the calculation throughout the energy range for a given wave vector $k$.