Computer simulation approach to reliability and accuracy in powder diffraction structure refinement

The frequency distribution of different parameters of a powder pattern can be directly sampled by analysing a population of simulated patterns produced by adding computer-generated noise to an exact calculated pattern. The procedure gives statistical estimators (mean, dispersion, correlations) of the parameters, which can be compared to the corresponding single-pattern estimates to test the performance of a strategy for data acquisition and structure analysis, to evaluate the bias introduced by wrong models and to clarify the amount of information actually contained in an experimental pattern. Examples are given for the simple structure of an almost completely inverted spinel (NiAl2O4).