An analysis of local and gradient-corrected correlation energy functionals using electron removal energies

Abstract

A comparison is made of various local and gradient-corrected correlation energy functionals, E_c(n,m), for positive, neutral and negative ions with atomic numbers between 1 and 30. The improvement in the total correlation energy, in _c, from the gradient corrected E_c(n,m) is not always transferred to the correlation energy differences, e.g. correlation energy contributions, Delta in _c, to ionisation potentials (IP) and electron affinities (EA). Particular attention is given to the 3d transition series, where none of the presently E_c(n,m) reproduce the experimental Delta in _c very well. An identity for differences in energy functionals of Vosko and Lagowski (1986) is used to express Delta E_c directly in terms of the number and spin magnetic moment density differences and 'effective potentials'. The trends in the IP and EA Delta in _c for the 3d transition series elements are analysed using this identity, and the inadequacies of presently available E_c(n,m) are discussed.