# Heavy-atom method

The figure shows how the structure factor is derived by vector addition of the scattered waves from the different contributing atoms in the unit cell. Consider the case of an atom with a very much higher scattering factor than any of the others $(\,\,f_0 >> \sum_i f_i \,\,)$; it is clear that the total phase angle φ will be small, and that the net phase of the structure factor differs very little from that of the heavy-atom component alone.