Pair distribution functions calculated from interatomic potential models using the General Utility Lattice Program

A new module has been developed for the widely used General Utility Lattice Program (GULP). The phonon-based theory developed by Chung & Thorpe [Phys. Rev. B (1999), 59, 4807–4812] to calculate pair distribution function (PDF) peak widths has been utilized to give a selection of commonly used correlation functions. A numerical library of neutron scattering information is now available within GULP, and is used to produce results that can be compared with neutron scattering experimental data. The influence of different phonon modes on the PDF can be assessed by excluding modes above or below a cut-off frequency. Results are presented for sample crystallographic systems, MgO, SrTiO₃ and α-cristobalite, as well as Ca_xSr_1−xTiO₃ at x = 0.5, which makes use of the capability to handle partial occupancies to compare different Ca/Sr ordering arrangements with a disordered model in which every Ca/Sr site has 50% occupancy of both species.