GENERALIZED RAYLEIGH-SCHRODINGER PERTURBATION-THEORY IN MATRIX FORM

The nested summation symbols (NSS) formalism is used as a starting poi nt to formulate a completely general Rayleigh-Schrodinger perturbation theory (RSPT) scheme. In order to make the theoretical framework prac tical from a computational point of view, the matrix form for the theo ry is given in every case. As a result, an algorithmic iterative recip e to compute eigenvalue and eigenvector corrections up to any order is described. Degenerate systems are also treated. At the same time the described procedure allows the computation of eigenvalue and eigenvect or derivatives with respect to a set of parameters.