Revisiting UF6, NpF6 and PuF6 for bonding and molecular surface analysis within density functional theory: Comparative study at the different theory levels with the same basis set

Abstract

UF6, NpF6 and PuF6 have been reexamined for their bonding characteristics and molecular surfaces. The bonding properties of these compounds were analyzed by calculating bond orders, partial charges, dipole moments, localized molecular orbitals, and topological properties. The bond orders increase with the atomic number (Z) of actinide as the bond lengths decrease. The partial charges, calculated by Atoms in Molecules (AIM) and Mulliken methods, and the bond dipole moment decrease with increasing Z. There is a fluctuation in the partial charge value for Np according to other charge models. The f character of the localized molecular orbital increases with Z. In general, the parameters obtained from topological analysis show an increase in the covalency across the period for U, Np and Pu. The molecular volume and surface obtained from surface analysis decrease with Z, which is consistent with the bond lengths. The molecular surface electrostatic potentials for intermolecular interactions decrease with Z according to surface analysis. The mass density and heat of sublimation data are interpreted based on molecular surface analysis results. All the density functionals and HERDB with the same basis set give consistent results for almost all the quantities calculated.