First-principles investigation of charge disproportionation in HoNio3 perovskite

We have investigated the electronic structure of HoNiO3 perovskite using first principles based on the density-functional theory. A comparison of electron-density map between orthorhombic and monoclinic structures indicated that there is only one type of Ni3+ state in the orthorhombic-metallic phase (space group Pbnm), and there are two types of Ni(3 - delta)+ and Ni(3 + delta)+ states in the monoclinic-insulating phase ( space group P2(1)/ n). The characteristic parameter of charge disproportionation delta is concerned with the non-bonding t(2g) band of partial density of states of Ni3d electron. delta is calculated to be 0.34 +/- 0.01, based on the changes of t(2g) band from orthorhombic to monoclinic phase.