Practical aspects and applications of some probabilistic formulae which estimate one-phase seminvariants

Some algorithms have been derived to calculate the expected values of one-phase seminvariants of first rank in space groups up to orthorhombic by a probabilistic approach [Giacovazzo (1978). Acta Cryst. A34, 562-576]. The method has been tested on several known structures. The results show how the method can secure a very reliable estimate for a limited number of one-phase seminvariants which can be used from the initial stages of phase determination. In addition, the estimated values can be used as a good figure of merit to select the correct K2 solution in a multisolution procedure.