Novel Electronic Structure of Nitrogen-Doped Lutetium Hydrides

First-principles density functional theory (DFT) calculations of Lu-H-N compounds reveal low-energy configurations of Fm$\overline{3}$m Lu$_{8}$H$_{23-x}$N structures that exhibit novel electronic properties such as flat bands, sharply peaked densities of states (van Hove singularities, vHs), and intersecting Dirac cones near the Fermi energy (E$_F$). These N-doped LuH$_3$-based structures also exhibit an interconnected metallic hydrogen network, which is a common feature of high-T$_c$ hydride superconductors. Electronic property systematics give estimates of T$_c$ for optimally ordered structures that are well above the critical temperatures predicted for structures considered previously. The vHs and flat bands near E$_F$ are enhanced in DFT+U calculations, implying strong correlation physics should also be considered for first-principles studies of these materials. These results provide a basis for understanding the novel electronic properties observed for nitrogen-doped lutetium hydride.