DFT Study of the Single-Band Layered TMO LiNbO$_2$

We establish using first principles methods that LiNbO$_2$ is a realization of a triangular lattice ``single band'' system. The bandwidth (less than 2 eV) suggests the interesting possibility of correlation effects that should be kept in mind. We present a tight-binding model for the valence band of LiNbO$_2$, composed primarily of Nb d$_{z^2}$ states, finding that intralayer second neighbor hopping $t_2 ~ 100$ meV is dominant over the significantly smaller first neighbor interactions $t_1 ~ 70$ meV. The nearest neighbor coupling is strongly modified by oxygen displacements, and the electron-phonon coupling may provide the coupling mechanism for superconductivity in Li-deficient samples ($T_c \approx 5$K). We will present the Nb-centered Wannier function, which provides insight into this unusual electronic structure. Calculations of the Born effective charges for the metal ions are also found to have anisotropy that reflects the layered nature of the electronic bonding. Their deviation from formal charge values indicates important covalent character, which is also evident in the Wannier function.