For cubic h1h2+k1k2+l12 cos pp= 2 (h12+k12+l1)(h2+k2+2 For orthorhombic h,h,, kk2 l1l2 2 b COS(= h k )2+(4)2]×( h2\2,k2 b CFor orthorhombic: [( ) ( ) ( ) ] [( ) ( ) ( ) ] cos 1 2 1 2 1 2 2 2 2 2 2 2 2 1 2 2 1 2 2 1 2 c l b k a h c l b k a h c l l b k k a h h + +  + + + +  = For cubic: ( )( ) cos 2 2 2 2 2 2 2 1 2 1 2 1 1 2 1 2 1 2 h k l h k l h h k k l l + + + + + +  =