  We describe the implementation of analytical Hartree-Fock gradients for
periodic systems in the code CRYSTAL, emphasizing the technical aspects of this
task. The code is now capable of calculating analytical derivatives with
respect to nuclear coordinates for systems periodic in 0, 1, 2 and 3 dimensions
(i.e. molecules, polymers, slabs and solids). Both closed-shell restricted and
unrestricted Hartree-Fock gradients have been implemented. A comparison with
numerical derivatives shows that the forces are highly accurate.
