Some consequences of the presence of antisymmetric atomic features in noncentrosymmetric structures

Noncentrosymmetric structures are considered in terms of a generalized substructure formulation. Inclusion of dispersion, bonding and anharmonicity leads to generalized expressions for Bijvoet ratios. Methods of numerically estimating the effects due to bonding and anharmonicity upon the Bijvoet ratios are suggested. Allowance for bonding and anharmonicity is shown to have wide implications for the breakdown of Friedel's law. Subsets of reflections that obey Friedel's law in the conventional approximation are now shown to violate it. These violations are of considerable importance for measuring antisymmetric contributions due to bonding and anharmonic thermal vibrations. The possibility that bonding effects will result in the appearance of Bijvoet differences in noncentrosymmetric structures of elements is explored.