1. The problem statement, all variables and given/known data Hi everybody. I am triying to do the next exercice: Given a unit cell of Ice X and knowing the positions of the atoms on it, find the expression of the structure factor for a difraction peak as a function of its Miller's index and the atomic form factors fO and fH. Will there be a systematic extinction? Would there be more extinctions if fO=fH 2. Relevant equations F=Σfi*erjHhkl In the ice X, there are two atoms of oxygen (0,0,0) and (0.5, 0.5, 0.5); the atoms of hydrogen are at (1/4, 1/4, 1/4), (3/4, 3/4, 1/4), (3/4, 1/4, 3/4) and (1/4, 3/4, 3/4) 3. The attempt at a solution F=fO*(1+expπ[h+k+l])+fH*(exp[(π/2)(h+k+l)]+exp[(π/2)(3h+3k+l)]+exp[(π/2)(3h+k+3l)]+exp[(π/2)(h+3k+3l)]) Here is where I don't know how to keep going; I have never seen something with two different atomic form factors. In theory we have seen the case where only the firs term is; in that case, I would say h+k+l=2n+1 so that 1+expπ[h+k+l] becomes zero; but I don't know how to solve this with a second kind of atom. Can anyone please help me? Thanks for reading.