Conservation of the spectral moments in the n-pole approximation
arXiv:cond-mat/9803276 · doi:10.1016/S0375-9601(98)00728-2
Abstract
A formulation of the Green's function method is presented in the n-pole approximation. Without referring to a specific model we give a general scheme of calculations that easily permits the computation of the "single-particle" Green's function in terms of the energy matrix. A theorem is proved which states that the moments of the spectral density function are conserved up to the order 2(n-l+1), where l is the order of the composite field. A comparison with the spectral density approach is also discussed.
12 pages, RevTeX