Face Centered Cubic (FCC) - There is one host atom at each corner, one host atom in each face, and the host atoms touch along the face diagonal (a = 2.8284r, Z = 4). This lattice is "closest packed", because spheres of equal size occupy the maximum amount of space in this arrangment (74.05%); since this closest packing is based on a cubic array, it is called "cubic closest packing": CCP = FCC.