Diffraction by Polycrystalline Fibers with Correlated Disorder

Theory is developed for describing diffraction from polycrystalline fibers of helical molecules, in which the constituent crystallites contain correlated lattice disorder and uncorrelated substitution disorder. The theory utilizes a recently reported description of cylindrically averaged diffraction by distorted lattices that is based in real space and uses an imposed correlation field to describe correlated disorder [Stroud & Millane (1996). Proc. R. Soc. London Ser. A, 452, 151-173]. The theory developed here is implemented as an efficient numerical algorithm for calculating diffraction patterns from fibers containing correlated disorder. Simulations are used to explore the effects of this kind of disorder and to characterize the disorder in a polynucleotide fiber whose diffraction pattern indicates its presence. This leads to a significant improvement in the agreement between the calculated and measured diffraction patterns over that from a model of only uncorrelated lattice disorder.