PNNL

Abstract

The structural and bonding properties of actinide (IV) oxalates, U(C2O4)2·6H2O and Pu(C2O4)2·6H2O, are investigated using the generalized gradient approximation (GGA) to spin-polarized density functional theory (DFT) with van der Waals (vdW) corrections. The GGA optimized structures, ground state magnetic moments, site-projected density of states, and Bader charges are reported. We calculate the energy differences between ferromagnetic (FM) and antiferromagnetic (AFM) spin configurations on the Pu or U sites to determine the preferred magnetic structure of these materials. For both U(C2O4)2·6H2O and Pu(C2O4)2·6H2O, the relaxed FM-spin structures were found to be higher in energy than the corresponding relaxed AFM-spin structures. The density of states based on AFM-spin configuration do not reveal a significant energy gap near the Fermi level of either system; however, hybridization between the actinide (Pu or U) 5f and O (2p) states is evident. Bader charge analysis also reveals significant covalent contributions in the An-O bonds of the actinide-oxalate layer of both U(C2O4)2·6H2O and Pu(C2O4)2·6H2O systems.