Effective medium theory for the normal state in orientationally disordered fullerides

An effective medium theory for studying the electronic structure of the orientationally disordered ${\mathit{M}}_3$ ${\mathrm{C}}_{60}$ fullerides is developed and applied to study various normal properties. The theory is based on a cluster-Bethe-lattice method in which the disordered medium is modeled by a three-band Bethe lattice, into which we embed a molecular cluster whose scattering properties are treated exactly. Various single-particle properties and the freqeuncy-dependent conductivity are calculated in this model, and comparison is made with numerical calculations for disordered lattices, and with experiment.