Revising structure descriptions and space groups from simulated structure factors

A method for space-group revision that does not require a comprehensive kno wledge of the International Tables for Crystallography is described. The st ructure factors of a crystal structure that has been refined in an incorrec t space group are generated from the atomic coordinates of the structure, a nd the simulated structure factors are re-indexed according to the suggesti ons of programs that check for metrical symmetry. The correct space group c an th en be identified from systematically-ab sent reflections and the diff raction symmetry, and the structure solved in the correct space group. Impl ementation of the method has revealed how it can also be used to assess the possibilities for systematic errors in doubtful structure determinations b y evaluating the refinement statistics associated with the use of calculate d reflections for one model as observations for the refinement of an altern ative model.