Novel lithium-nitrogen compounds at ambient and high pressures

Using ab initio evolutionary simulations, we predict the existence of five novel stable Li-N compounds at pressures from 0 to 100 GPa (Li(13)N, Li(5)N, Li(3)N(2), LiN(2), and LiN(5)). Structures of these compounds contain isolated N atoms, N(2) dimers, polyacetylene-like N chains and N(5) rings, respectively. The structure of Li(13)N consists of Li atoms and Li(12)N icosahedra (with N atom in the center of the Li(12) icosahedron) – such icosahedra are not described by Wade-Jemmis electron counting rules and are unique. Electronic structure of Li-N compounds is found to dramatically depend on composition and pressure, making this system ideal for studying metal-insulator transitions. For example, the sequence of lowest-enthalpy structures of LiN(3) shows peculiar electronic structure changes with increasing pressure: metal-insulator-metal-insulator. This work also resolves the previous controversies of theory and experiment on Li(2)N(2).