  Atomic scale simulations are a key element of modern science in that they
allow to understand, and even predict, complex physical or chemical phenomena
on the basis of the fundamental laws of nature. Among the different existing
atomic scale simulation approaches, molecular dynamics (MD) has imposed itself
as the method of choice to model the behavior of the structure of materials
under the action of external stimuli, say temperature, strain or stress,
irradiation, etc. Despite the widespread use of MD in condensed matter science,
some basic material characteristics remain difficult to determine. This is for
instance the case of the long-range strain tensor in heavily disordered
materials, or the quantification of rotated crystalline domains lacking clearly
defined boundaries. In this work, we introduce computational diffraction as a
fast and reliable structural characterization tool of atomic scale simulation
cells. As compared to usual direct-space methods, computational diffraction
operates in the reciprocal-space and is therefore highly sensitive to
long-range spatial correlations. With the example of defective UO2, it is
demonstrated that the homogeneous strain tensor, the heterogeneous strain
tensor, the disorder, as well as rotated crystallites are straightforwardly and
unambiguously determined. Computational diffraction can be applied to any type
of atomic scale simulation and can be performed in real time, in parallel with
other analysis tools. In experimental workflows, diffraction and microscopy are
almost systematically used together in order to benefit from their
complementarity. Computational diffraction, used together with computational
microscopy, can potentially play a major role in the future of atomic scale
simulations.
