> Dear Alberto, if your data are of high resolution it is not impossible to refine the occupancy, but it depends on the contrast or difference of b length (the correspondence of the scattering factor in X-ray) of the elements whose occupancy you want to refine. Besides, it also depends on how many different atoms you want to refine in each site; in fact, if you want to refine more than two atoms in each site you should combine x-ray with neutron data.
Francesco
