Exact distorted-wave approach to multiple-scattering theory for general   potentials
  We present a new approach to real-space multiple-scattering theory for molecules and clusters, based on the two-potential (distorted-wave) Lippmann-Schwinger equation formalism. Our approach uses a recently developed form [D. L. Foulis, Phys. Rev. A70, 022706 (2004)], for the partial-wave expansions of the exact time-independent single-particle Green function for a general potential, to solve exactly the scattering problem for the distorting potential. The multiple-scattering problem for the full multicenter molecular potential is then developed along familiar lines, within a partition of space consisting of non-overlapping atomic spheres, but relative to the distorting potential. To achieve this some new general Green-function re-expansion formulas are derived, as well as further developments of our earlier partial-wave expansions. Based on the division of the multicenter molecular potential into the non-singular distorting potential and a remaining singular part we develop explicitly the secular equations of our approach and prove a result concerning the symmetry of the atomic matrices. The new secular equations are similar in overall form to those of related methods, requiring coupled radial Schr\"odinger-equation solutions for each atomic center, together with atomic-sphere surface integrals, but no volume integrals. We treat both continuum (scattering) states and bound states within the same framework, and consider also the case of an outer sphere. 
D. L. Foulis