The phase problem: we dont know what phases to use to add up all of the contributing waves, BIG PROBLEM Px2=7222 7-2r(hx+y+) atoms Fk lexp(iah )=Fnk)=>f, exp[2T.i(h u)+kyu+lx) observable amplitude atomic scattering factor-related the phase of f is determined by the to electron density around atom j x ,y and z coordinates of the atoms What we observe is Inki a Fk l2 we cant measure the phases directly Get phases from molecular replacement, or heavy atom methodsThe Phase Problem: we don’t know what phases to use to add up all of the contributing waves. BIG PROBLEM. | Fhkl | exp( i αhkl ) = observable amplitude atomic scattering factor - related the phase of F is determined by the to electron density around atom j x, y and z coordinates of the atoms What we observe is Ihkl α |Fkhl|2 we can’t measure the phases directly Get phases from molecular replacement, or heavy atom methods