Data processing-Indexing

The determination of cell parameters is so fundamental that: 1) if no cell has been identified, the execution of the successive steps of the crystal structure solution process is impossible; 2) if a wrong cell has been used the correct solution is unreachable. Therefore extreme attention must be focused on the indexing step, and indexing has been called a "gateway technology". Starting in the early 1970s, the increasing interest in powder indexing and the progress, in terms of both methods and algorithms, have strongly contributed to opening the door to modern applications of powder diffraction techniques. The availability of a quite large number of software packages, based on different strategies of indexing, enables the scientist interested in solving crystal structures to switch from one program to another one in case of failure, so increasing the possibility of success. In some cases indexing is still a challenging process. Good quality data is necessary and careful inspection of each indexing step, in particular in the selection of the experimental peak positions to be used, is advised.