Since the stoichiometry of the salt is 2:1, we must fill all of the tetrahedral holes (the FCC structure gives four selenides, thus we need eight lithiums). will occupy the latice points that define ...

The monoclinic structure has two unit cells. The primative cell (P) has fractional lattice points at the corners of the cell, and the base-centered cell (C) has additional fractional lattice points at ...