New criteria for use in crystal structure refinement

Abstract

Two new types of discrepancy factors which are mean values of fractional discrepancies of observed and calculated quantities are suggested. One of them is defined by [unk] where |F_o| and |F_c| are the observed and calculated structure factors, N is the total number of reflections and 'or' in the denominator means |F_o| or |F_c| whichever is larger, is to be used in the summation. The other index R" is similar to R' but uses intensities instead of amplitudes. Theoretical values of R' and R" are derived for a completely random structure, both for centrosymmetric and non-centrosymmetric cases. Tests on a practical case and comparison with the conventional discrepancy index are also reported.