  Many functional materials are today synthesised in form of nanoparticles
displaying preferred orientation effects to some small or large extent. The
analysis of diffraction data of such kind of systems is best performed in the
framework of the total scattering approach that prescinds from translation
symmetry assumptions. We therefore derived modified expressions for the most
common total scattering functions, in particular the Debye Scattering Equation
(DSE) that yields the texture-averaged differential cross section as a function
of atomic coordinates and texture parameters. The modified DSE encodes
higher-order even spherical Bessel functions which account for the texture
effect. Selection rules arising from experimental geometries and symmetries are
discussed. In addition the duality of the texture effect is introduced showing
the effects of texture on both the I(Q) and G(r). The paper includes several
definitions and appendices which are meant to be useful for those involved in
the development of crystallographic computing.
