A set of GaAs whisker crystallites in the shape of hexagonal prism with the axis along the [111] direction have been modeled as well as constructions consisting of such prisms. For these model samples XRD patterns have been calculated. Basing on the calculated XRD pattern analysis, a fitting configuration of prismatic fragments has been built for an atomic array obtained with the help of applying molecular dynamics techniques to the initial model prismatic GaAs crystallite.