title: Density functional investigations of the properties and thermochemistry of UF6 and UF5 using valence-electron and all-electron approaches.
abstract: The structural properties and thermochemistry of UF6 and UF5 have been investigated using both Hartree-Fock and density functional theory (DFT) approximations. Within the latter approach, the local spin-density approximation, the generalized gradient approximation, and hybrid density functionals were considered. To describe the uranium atom we employed small-core (60 electrons) and large-core (78 electrons) relativistic effective core potentials (RECPs), as well as the all-electron approximation based on the two-component third-order Douglas-Kroll-Hess Hamiltonian. For structural properties, we obtained very good agreement with experiment with DFT and both large and small-core RECPs. The best match with experiment is given by the hybrid functionals with the small-core RECP. The bond dissociation energy (BDE) was obtained from the relative energies of the fragments [UF6 --> UF5 + F], corrected for zero-point energy and spin-orbit interaction. Very good agreement was found between the BDE obtained from all-electron calculations and those calculated with the small-core RECP, while those from the large-core RECP are off by more than 50%. In order to obtain good agreement with experiment in the BDE it is imperative to work with hybrid density functionals and a small-core RECP.
authors.affiliation: Los Alamos National Laboratory, Theoretical Division, MS B268, New Mexico 87545, USA.
authors.forename: Enrique R
authors.initials: ER
authors.lastname: Batista
authors.forename: Richard L
authors.initials: RL
authors.lastname: Martin
authors.forename: P Jeffrey
authors.initials: PJ
authors.lastname: Hay
authors.forename: Juan E
authors.initials: JE
authors.lastname: Peralta
authors.forename: Gustavo E
authors.initials: GE
authors.lastname: Scuseria