A direct method for inferring planar disorder and structure from X-ray diffraction studies Dowman P. Varn Max-Planck-Institut für Physik komplexer Systeme Santa Fe Institute Department of Physics and Astromony, University of Tennessee, Knoxville Geoffrey S. Canright Telenor Research and Development Department of Physics and Astronomy, University of Tennessee, Knoxville James P. Crutchfield Computational Science & Engineering Center & Physics Department, University of California, Davis Santa Fe Institute Abstract: In a recent publication Phys. Rev. B 66 174110 (2002) we introduced a new technique for discovering and describing planar disorder in close-packed structures directly from their diffraction spectra. Here we provide the theoretical development behind those results, adapting computational mechanics to describe one-dimensional structure in materials. We show that the resulting statistical model of the stacking structure---called the e-machine---allows the calculation of measures of memory, structural complexity, and configurational entropy. By way of contrast, we give a detailed analysis of the current alternative approach, the fault model, and offer several criticisms. In the limit of weak faulting, we demonstrate how various architectural features of the e-machine correspond to well-known structural faults in two common types of crystal, 2H and 3C. The methods developed here can be adapted to a wide range of experimental systems in which spectroscopic data is available. A copy of this paper in pdf format: A direct method for inferring planar disorder and structure from X-ray diffraction studies Citation: D.P. Varn, G. S. Canright and J.P. Crutchfield, submitted to Acta Crystallographica A Referee Reports