Sign distribution of two-phase structure invariants

An empirical investigation of the distribution of Friedel-pair two-phase structure invariants has been reported by Guo & Hauptman [Chin. Sci. Bull. (1989), 34, 137-141]. In the present paper their sign distributions are calculated for some small molecules and for a protein. The statistical figures show that there exists a strong tendency towards positive values for the signs of the two-phase structure invariants. It is anticipated that Hauptman's formula [Acta Cryst. (1982), A38, 632-641] may be good enough to estimate statistically the signs of the two-phase structure invariants for these model crystals.