Electron density is not spherical: the many applications of the transferable aspherical atom model

n the simplest approach and at low resolution, the electron density of an atom can be approximated by a sphere. However, the resolutions currently achieved in X-ray macromolecular crystallography reach atomic resolutions, where a more sophisticated approach is inevitable. This review summarizes the available electron density and scattering factor models and their applications with emphasis on the transferable aspherical atom model (TAAM).