A perturbation theory in terms of reduced matrices
John E. Harriman · NASA STI Repository (National Aeronautics and Space Administration) · 1970
A simple p e r t u r b a t i o n thepry &,as been developed f o r reduced d e n s i t y matrices which are known t o b e N-representable as functions of some set of independent parameters.Formulas are presented for s i n g l e and d0ubJ.eperturbations through second order.Extension t o higher order would b e possible, b u t involved.The r e s u l t s do ngt depend e x p l i c i t l y on t h e order of t h e d e n s i t y matrix, and when t h e N-particle d e n s i t y matrix i s used, t h e formulas can b e reduced t o those of conventional Rayleigh-SchrkJdinger theory.Details are given f o r t h e s p e c i a l cases of spin-unrestricted or extended SCF density matrices and C I or optimized multiconfiguratlon density matrices which are known t o b e N-representable.