DISCUS: A program for diffuse scattering and defect-structure simulation

The program DISCUS is a versatile tool for the analysis of diffuse scattering and for defect structure simulations. The model structure can be created from an asymmetric unit of a unit cell or a complete structure can be read from a file. A Fortran77 style interpreter that includes IF statements and various loops combined with predefined defect types like thermal displacements, waves and microdomains allows one to create all sorts of defect structures. The Fourier-transform segment of the program allows one to calculate neutron as well as X-ray intensities including isotropic temperature factors and anomalous scattering. The calculation of the inverse and difference Fourier transform as well as the Patterson function is also implemented. A model structure can be 'fitted' to observed diffuse scattering data by reverse Monte Carlo (RMC) simulations. The RMC segment allows one to model displacive as well as occupational disorder. The program is completely written in Fortran77 and the source code is available via the World Wide Web.