Powder diffraction pattern fitting and structure refinement by means of the CPSR v.3.1 software package

An updated version of the CPSR software package for powder pattern fitting and structure refinement offers major advantages over previous versions. An optional use of the new figure-of-merit function, that takes into account a systematic behaviour of residuals, allows users to reduce the effect of local correlations at the full-profile fitting stage, thus providing more reliable estimates for integrated intensities and their deviances. The structure refinement stage in such a case yields accurate values for estimated standard deviations of structural parameters since, in addition, model errors affecting calculated integrated intensities are taken into consideration. Furthermore, the new CPSR version is customized for a variety of constant-wavelength neutron and X-ray diffraction techniques and is equipped with an enhanced menu structure. Graphical on-screen-controlled support allows users to follow the progress of a fitting procedure over any region of a powder pattern. The program performance is illustrated using the neutron diffraction data file for PbSO4 distributed during the Rietveld refinement round robin, organized by the IUCr Commission on Powder Diffraction.