“…Most crystalline structures are non-ideal, e.g., they contain defects. Statistical dynamical diffraction theory (in the case of a plane-wave illumination) (Bushuev, 1989;Punegov, 1990Punegov, , 1991Punegov, , 1993Pavlov & Punegov, 1998, 2000 using Takagi's equations (Takagi, 1962) is one possible way to describe X-ray dynamical diffraction in such structures. However, Darwin's theory (Darwin, 1914a,b), which was originally developed for an ideal crystal, can also be modified for use with non-ideal crystals.…”