The mean-square Friedel intensity difference in P1 with a centrosymmetric substructure

Acta Cryst. (2007). A63, 257–265 [doi:10.1107/S0108767307002802]

For non-centrosymmetric crystals one may observe and calculate a Friedel difference in intensity between I(hkl) and I(-h-k-l) due to the action of resonant scattering. However, it is known that a non-centrosymmetric crystal structure of elemental Se shows no Friedel differences and that a centrosymmetric substructure does not necessarily decrease the Friedel differences. Flack and Shmueli have undertaken a detailed statistical analysis of rms Friedel differences. A resulting Bijvoet intensity ratio provides an estimate of the rms Friedel difference relative to the mean intensity. Applications are in the fields of structure solution by MAD, SAD, etc. and in absolute-configuration determination.