Simulating neutron protein crystallography experiments: applications to the development of the NMX instrument at ESS

Monte Carlo neutron ray-tracing simulations of time-of-flight (TOF)–Laue neutron macromolecular crystal diffraction ( n -MX) using the McStas software package were performed for the upcoming NMX Macromolecular Diffractometer at the European Spallation Source. Splitting neutron rays that arrive at the crystal leads to dramatic improvements in event formation with minimal computational overhead. The simulated event-probability data were sampled using a new single-pass weighted reservoir-sampling method, and processed like real n -MX data using DIALS . The effects of air and beamstop scatter on simulated data were investigated.