Reciprocal-space instrumental effects on the real-space neutron atomic pair distribution function

An atomic pair distribution function (PDF) neutron powder diffraction round-robin experiment was performed on six diffractometers at three spallation sources. Instrument-specific effects on the real-space PDF were investigated, such as finite measurement range, the instrument resolution and the asymmetric shape of diffraction peaks. Two illustrative samples, a perfectly long-range-ordered element, Pb, and a locally strained alloy ZnSe_0.5Te_0.5, were measured at low temperatures. Various aspects of the PDF were explored, either qualitatively by direct comparison or quantitatively via structural modelling. Future implementation of modelling codes incorporating some of these instrumental effects are also discussed.