Nature of the hole states in Li-doped NiO

We have performed density functional calculations on Li${}_{0.125}$Ni${}_{0.875}$O using both the HSE06 hybrid functional and the density functional theory (DFT) $+$ $U$ method. Contrary to previous calculations, both methods show that the system is better described with the hole localized on the nickel ion (which is thus formally Ni${}^{3+}$) rather than in the oxygen valence band. We discuss the experimental results in the light of this finding and show that it is consistent with the available data.

Figure 1

Local density of states of the undistorted and distorted Ni in the optimized LiNi${}_7$O${}_8$ supercell using the HSE06 functional (left) and $\mathrm{GGA}+U$ (right).

Figure 2

Density of states of NiO and Li${}_{0.125}$Ni${}_{0.875}$O for the HSE06 functional (left) and $\mathrm{GGA}+U$ (right) showing both relaxed and unrelaxed cases for Li${}_{0.125}$Ni${}_{0.875}$O. Note in the $\mathrm{GGA}+U$ density of states for Li${}_{0.125}$Ni${}_{0.875}$O, the Ni and O states overlap completely at the spin-up peak around 0.5 eV.

Figure 3

Calculated oxygen empty states (left) of Li${}_x$Ni${}_{1-x}$O with $x$ $=$ 0, 0.125 (offset for clarification) using $\mathrm{GGA}+U$ compared to experimental result (right) from Ref. 11. Note the peak (circled) in the experimental data for $x$ $=$ 0.4.

Figure 4

Charge-density contour map ($e$/Å${}^3$) of hole states in the (100) plane for Li${}_{0.125}$Ni${}_{0.875}$O. Results shown for the HSE06 functional; those for the $\mathrm{GGA}+U$ method are indistinguishable.