Difference Fourier syntheses in fiber diffraction

Abstract

Theory applying to difference Fourier syntheses from fiber diffraction data is developed, including the calculation of expected peak heights and noise levels. The signal-to-noise ratio in fiber diffraction difference maps is much lower than in crystallography, because of the multi-dimensional nature of fiber diffraction data, but it is shown by means of examples from tobacco mosaic virus that high-order difference syntheses, for example using coefficients analogous to crystallographic 6Fobs - 5Fcalc, can clearly reveal differences between an observed structure and a model. 'Omit' maps, calculated from models by omitting a region under particular scrutiny, are of limited use in fiber diffraction, but maps calculated from hybrid coefficients derived from both full and partial models have some applications.