The reliability index R-2 as a versatile tool in structure analysis of inorganic and small molecular compounds
Beurskens PT, Israel R, de Gelder R, Beurskens G, de Graaff RAG
JOURNAL OF APPLIED CRYSTALLOGRAPHY 34: 178-186 Part 2 APR 1 2001

Abstract:
Applications of R-2 in small-molecule crystallography are described. Ways of using R-2 to evaluate initial models of a structure are discussed. These models, obtained from Patterson methods, are usually small. They may include one or more heavy atoms and pseudosymmetry is sometimes present in the model. The R-2 criterion is used also to identify misplaced atoms prior to the start of the expansion process. Finally, R-2 is used during structure expansion by the application of phase refinement or Fourier methods. Details of the procedures of extension, as well as the role of R-2 therein, are presented and evaluated. Results obtained with various test structures are discussed.