title: Simple approximants for natural orbitals of harmonium.
abstract: Simple approximations to the natural orbitals (NOs) of harmonium with enforced correct short- and long-range asymptotics yield accurate bounds for the NO occupancies. In particular, expressions involving Pade approximants with just one variational parameter are capable of producing the largest NO occupancies with accuracy better than 10(-4). The comparison of two cases with different coupling strengths omega (1.948 51<n<1.948 60 for omega=12 and 1.821 24<n<1.821 29 for omega=110) indicates that the bounds actually become tighter with the increasing extent of correlation. The expressions derived for the most strongly occupied NOs can be readily generalized to all natural orbitals of harmonium.
authors.affiliation: Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland. jerzy@kyoko.chem.fsu.edu
authors.forename: Jerzy
authors.initials: J
authors.lastname: Cioslowski
authors.forename: Marcin
authors.initials: M
authors.lastname: Buchowiecki