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

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.