Multiple scattering theory rid of free-electron poles

The way out of the plaguing omnipresence of free-electron singularities in multiple scattering theory is presented. Both a supermatrix approach and a subtraction procedure are outlined. This opens the largely unexplored field of the electronic structure of interstitials and other non-lattice-site defects. Examples of the latter are the Frenkel pair defect and a defect corresponding to a migrating atom halfway along its jump path, being relevant to the process of electromigration induced failure. The ideas presented facilitate the up to now cumbersome calculations of electronic properties of other defects in dilute alloys as well.