title: Evaluation of <S2> in density functional theory.
abstract: The evaluation of <S2> in density functional theory (DFT) is considered. Wang et al. [J. Chem. Phys. 102, 3477 (1995)] have derived an approximate, local density expression for <S2> and in the present study their formula is evaluated using densities from unrestricted Hartree-Fock (UHF) and a range of DFT exchange-correlation functionals. The results are compared with those obtained by evaluating the conventional UHF expression using the Kohn-Sham orbitals, which is appropriate for the noninteracting system. A generalized gradient approximation for <S2> is then proposed and investigated.
authors.affiliation: Department of Chemistry, Duke University, North Carolina 27708, USA.
authors.forename: Aron J
authors.initials: AJ
authors.lastname: Cohen
authors.forename: David J
authors.initials: DJ
authors.lastname: Tozer
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Handy