Solving Crystal Structures from Powder Data. IV. The Use of the Patterson Information for Estimating the |F|'s

The positivity of the Patterson function is used as prior information for the decomposition of a powder diffraction pattern. An automatic procedure is described which, integrated with the Le Bail method, is able to provide estimates of |F| values that are often remarkably better than those obtained by application of standard techniques. The procedure, implemented in a computer program, has been applied to a set of test structures (experimental data); the results show that, particularly for structures with some heavy atoms, the new estimates of the structure-factor moduli are far better (on average) than those obtained via the default application of EXTRA [Altomare et al. (1995). J. Appl. Cryst. 28, 842-846]. 1. Symbols and abbreviations The papers by Altomare, Carrozzini et al. (1996), Altomare, Foadi et al. (1996) and Carrozzini et al. (1997) are referred to as papers I, II and III, respectively.