title: Combining two-body density correlation functionals with multiconfigurational wave functions using natural orbitals and occupation numbers.
abstract: We propose a procedure that combines multiconfigurational (MC) wave functions with two-body density correlation functionals by transforming the latter into functionals of the MC natural orbitals and occupation numbers. The method is tested with the spectroscopic constants of a set of 11 diatomics, the diradical-involved automerization barrier of cyclobutadiene, the energy difference between triplet and open-shell singlet states in He and the methylene molecule, and the magnetic coupling constants of several systems, such as NiO, KNiF(3), K(2)NiF(4), La(2)CuO(4), alpha-4-dehydrotoluene, 1,1('),5,5(')-tetramethyl-6,6(')-dioxo-3,3(')-biverdazyl, [Cu(2)Cl(6)](-2), copper(II) acetate monohidrate and H-He-H. The procedure is applied to the Colle-Salvetti [Theor. Chim. Acta 37, 329 (1975); 53, 55 (1979)], functional and to a size-consistent functional depending on the on-top pair density (F1-5-N(eff)). On average, the best results are provided by the transformed F1-5-N(eff) [J. Chem. Phys. 114, 2022 (2001)] functional.
authors.affiliation: Departamento de Química-Física, Universidad de Alicante, Alicante E-03080, Spain. aj.perez@ua.es
authors.forename: Angel J
authors.initials: AJ
authors.lastname: Pérez-Jiménez
authors.forename: José M
authors.initials: JM
authors.lastname: Pérez-Jordá
authors.forename: Juan C
authors.initials: JC
authors.lastname: Sancho-García