Crystal structure refinement

Abstract The determination of a crystal structure consists of several steps of which refinement comes towards the end. After crystal growth, data collection, data reduction, absorption correction, and solution of the phase problem, the crystallographer has obtained atomic coordinates for some or all non-hydrogen atoms. Frequently, the atom types assigned to some of these coordinates are incorrect or no atom types have been assigned at all. In addition, the coordinates in the first solution are usually not very accurate and many details of the structure are yet to be determined. The way to get from the first solution to the final accurate and publishable model is called refinement. This chapter explains how structure refinement is performed by SHELXL. This includes the concept of constraints, restraints, and free variables as well as calculating structural parameters such as bond lengths and angles.