Hi all, structure factor is 2πi(hx+ky+lz), (hkl)is plane index, and (xyz) is index within a unit cell of real lattice. For example, we are now calculating FCC's structure factor. In general, textbook taught us using convention unit cell of FCC( that is FCC in form of cubic) to index (xyz). so we got (xyz)=(000), (1/2 1/2 0), (1/2 0 1/2),..... But what if we use FCC's primitive unit cell instead of convention unit cell? Then (xyz) will be (000) only, and systematic absence will not happen. So what is wrong in my idea? Thanks!