NXFit: a program for simultaneously fitting X-ray and neutron diffraction pair-distribution functions to provide optimized structural parameters

NXFit is a program for obtaining optimized structural parameters from amorphous materials by simultaneously fitting X-ray and neutron pair-distribution functions. Partial correlation functions are generated in Q space, summed and Fourier transformed for comparison with the experimental data in r space. NXFit uses the Nelder-Mead method to vary a set of `best guess' parameters to achieve a fit to experimentally derived data. The output parameters from NXFit are coordination number, atomic separation and disorder parameter for each atomic correlation used in the fitting process. The use of NXFit has been demonstrated by fitting both X-ray and neutron diffraction data from two quite different amorphous materials: a melt-quenched (Na₂O)_0.5(P₂O₅)_0.5 glass and a (TiO₂)_0.18(SiO₂)_0.82 sol-gel.