Measurability of Bijvoet differences in triclinic, monoclinic and orthorhombic crystals

Theoretical expressions for the measurability of Bijvoet differences have been derived for triclinic, monoclinic and orthorhombic crystals containing p (= 1 or 2) anomalous scatterers and many normal scatterers per asymmetric unit. Results for the many- atom cases (i.e. P = MN and MC cases) in space group P1 are also obtained. The theory takes into consideration the effect of data truncation due to unobserved reflections. The measurability values for the various cases are given in the form of compact tables as functions of the relevant parameters k and σ²₁. The theoretical results are also used to discuss briefly the following aspects. (i) The effect of k and σ²₁ on the measurability. (ii) Measurability to be expected in the heavy-atom derivatives of proteins with Cu Kα radiation. (iii) A comparison of the measurabilities in Sm derivatives of a protein for Cu Kα and for a wavelength (λ = 1.8448 Å) at which the anomalous scattering effect has been observed to be the largest. It is also found that in the case of the heavy-atom derivatives of proteins measurability is strongly influenced by variation in σ²₁.