Energy-linearized variational cellular method for large molecules and solids

Multiple scattering theory (MST) is the mainstay of Kohn-Sham calculations of the electronic structure of solids and alloys. MST formalism solves one-electron equations within each atomic cell, using a Green function to propagate solutions across cell boundaries, while standard methodology for molecules expands wave functions in a Gaussian orbital basis. An energy-linearized version of MST (LMTO) is efficient but restricted to an atomic-sphere model. Full-potential MST extends the formalism to space-filling Wigner-Seitz polyhedra. The variational cellular method (VCM) solves full-potential equations, replacing Green-function propagation (structure constants) by variational matching at the interfaces of adjacent atomic cells. VCM provides a common formalism for molecules and solids but cannot easily be converted to an energy-linearized method. A new variational principle is derived here that extends the VCM to a straightforward procedure for energy linearization. This formalism eliminates false solutions from the VCM.