Abstract
In this work, the electronic structure and properties of NASICON-structured A(4)V(2)(PO(4))(3), where A = Li, Na, K were studied using hybrid density functional theory calculations. The symmetries were analyzed using a group theoretical approach, and the band structures were examined by the atom and orbital projected density of states analyses. Li(4)V(2)(PO(4))(3) and Na(4)V(2)(PO(4))(3) adopted monoclinic structures with the C2 space group and averaged vanadium oxidation states of V+2.5 in the ground state, whereas K(4)V(2)(PO(4))(3) adopted a monoclinic structure with the C2 space group and mixed vanadium oxidation states V+2/V+3 in the ground state. The mixed oxidation state is the least stable state in Na(4)V(2)(PO(4))(3) and Li(4)V(2)(PO(4))(3). Symmetry increases in Li(4)V(2)(PO(4))(3) and Na(4)V(2)(PO(4))(3) led to the appearance of a metallic state that was independent of the vanadium oxidation states (except for the averaged oxidation state R32 Na(4)V(2)(PO(4))(3)). On the other hand, K(4)V(2)(PO(4))(3) retained a small band gap in all studied configurations. These results might provide valuable guidance for crystallography and electronic structure investigations for this important class of materials.