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 face centered cubic (FCC) unit cell begins ... In other words, if we were to place an atom in each indentation, they would not all fit. Because of this, the second layer will only cover half of ...