6. Refinement of a crystallographic structure

The aim of refining a crystallographic structure is not only to improve the model constructed in terms of atomic positions in the previous steps, but also to determine the parameters characterizing the movements of the atoms, in order to best represent the structure(s) present in the crystal. Generally speaking, the refinement of a biological macromolecule is a process of non-linear optimization of a certain function (to be defined) dependent on parameters and based on observations.