Density-cumulant functional theory

摘要

Starting point is the energy expectation value as a functional of the one-particle density matrix gamma and the two-particle density cumulant lambda_2.We decompose gamma into a best idempotent approximation kappa and a correction tau,that is entirely expressible in terms of lambda_2.So we get the energy E as a functional of kappa and lambda_2,which can be varied independently.Approximate n-representability conditions,derived by perturbation theory are imposed on the variation of lambda_2.A nonlinear system of equations satisfied by lambda_2 is derived,the linearized version of which turns out to be equivalent to the coupled electron-pair approximation,variant zero.The start for kappa is Hartree-Fock,but kappa is then updated to become the best idempotent approximation of gamma.Relations to density matrix functional theory and Kohn-Sham type density functional theory are discussed.