be regarded as a fcc lattice with a two-atom basis. The basis atoms are located at (000) and a(ll1 , and the 0 crystal lattice constant a is 5.43 A [89L]. Figure l.l(a) shows the silicon crystal structure. Pure silicon exhibits full cubic symmetry and belongs to the 4, point group. The first Brillouin zone for the fcc lattice is a "truncated