First-principle calculations for electronic structure and bonding properties in layered Na₂Ti₃O₇

First-principles calculations of Na₂Ti₃O₇ have been carried out with density-functional theory (DFT) and ultrasoft pseudopotentials. The electronic structure and bonding properties in layered Na₂Ti₃O₇ have been studied through calculating band structure, density of states, electron density, electron density difference and Mulliken bond populations. The calculated results reveal that Na₂Ti₃O₇ is a semiconductor with an indirect gap and exhibits both ionic and covalent characters. The stability of the (Ti₃O₇)^2- layers is attributed to the covalent bonding of strong interactions between O 2p and Ti 3d orbitals. Furthermore, the O atoms located in the innerlayers interact more strongly with the neighboring Ti atoms than those in the interlayer regions. The ion-exchange property is due to the ionic bonding between the Na⁺ and (Ti₃O₇)^2- layers, which can stabilize the interlayers of layered Na₂Ti₃O₇ structure.