Ab-initio Studies of the Electronic Structures of the Hexavalent Uranium Compounds K2UO4 and Na4UO5

Abstract

Band theoretical results within the density functional theory are reported for the uranates K2UO4 and Na4UO5. The two structures are differentiated respectively by uranyl and reverse uranyl-type short U-O distances characterizing the UO6 octahedra, as also reflected by larger compressibility and stability of the potassium-based uranate derived from energy-volume equations of states and the cohesive energy. A larger ionic character of Na4UO5 is inferred from comparative Bader charge analyses. The two uranates are insulators with a larger band gap and less extended valence and conduction bands for Na4UO5. Chemical bonding shows major interactions for U-O versus Na,K-O and is further differentiated as a function of the distances. The band structure results confirm the hexavalent character of the uranium atoms.