Abstract

The classical method of phase determination from Bijvoet inequalities is applied to the phase hk = 1/2(hk -- ) of the triple product hk FhFkF. The phase-determining formula is then (in the case of a centrosymmetric configuration of anomalous scatterers): sin hk = in which hk is the contribution from the imaginary part of the complex double Patterson function to hk, and | 0hk2 =1/2(| hk|2 + | |2) - | hk|2. It is shown that hk contains an important term, i.e. the contribution from the origin peak of the double Patterson function, which is independent of the positions of the anomalous scatterers. A test calculation on a structure in P1, containing two Br ions, shows that, in fact, the phases of the triple products can be determined without introducing any a priori knowledge about the positions of the anomalous scatterers, provided an appropriate scaling procedure is applied.