Multishell method: Exact treatment of a cluster in an effective medium

摘要: A method is presented for the exact determination of Green's function a cluster embedded in given effective medium. This method, multishell applicable even to systems with off-diagonal disorder, extended-range hopping, multiple bands and/or hybridization, and computationally practicable any system described by tight-binding or interpolation-scheme Hamiltonian. It allows one examine effects local environment on densities states site spectral weight functions disordered systems. For analytic medium characterized non-negative density yields functions. Previous methods used calculation have not been exact. The results numerical calculations model show that best these previous can lead substantial errors, at least small clusters two- three- dimensional lattices. These also fluctuations large functions, cases which single-site coherent-potential approximation an accurate overall states.