In addition to the approximate atomic x, y, z-coordinates, there is another factor influencing the magnitudes of the structure factors - thermal motion. Even though the structure determination is done on the solid phase, the atoms still have some thermal motion (vibration and rotation). For example, in the organic molecule shown below, it might be expected that atoms on the periphery of the molecule would experience more thermal vibration that atoms in the interior of the molecule:

Particularly, the methoxy and t-butyl carbons would be expected to undergo a relatively greater amount of thermal vibration. This thermal effect is introduced into the structure factor equation by a factor that serves to attenuate the atomic scattering factor where the temperature factor, B, is related to the mean-square amplitude of vibration As B increases, the scattering power of atom j (f_j) decreases.