You can find here a collection of C/C++ tools that work with atomistic models.

debyer

The program takes as an input a file with positions of all the atoms in the virtual sample (up to tens of millions of atoms, perhaps even more) and can output x-ray and neutron powder diffraction pattern, total scattering structure function, pair distribution function (PDF) and related functions (RDF, reduced PDF).

Although the program can take a unit cell as input, there are more suitable programs to calculate a diffraction pattern of a perfect crystal.

dbr_extend

Modifies atomistic configurations. For example, it can extend the system, cut out a slab from the system, create a supercell or shift all the atoms under PBC. In some of the tasks, like extending the system, local periodicity of the structure is automatically determined first.

dbr_conv

Converts between a few file formats (XMOL xyz, AtomEye cfg, DL_POLY CONFIG, LAMMPS data file, PDB).

dbr_bonds

Calculates coordination number of atoms, distribution of bond lengths and angles between bonds.

and a few unfinished or undocumented tools.