DISCUS - A PROGRAM FOR DIFFUSE-SCATTERING AND DEFECT-STRUCTURE SIMULATION

The program DISCUS is a versatile tool for the analysis of diffuse sca ttering and for defect structure simulations. The model structure can be created from an asymmetric unit of a unit cell or a complete struct ure can be read from a file. A Fortran77 style interpreter that includ es IF statements and various loops combined with predefined defect typ es like thermal displacements, waves and microdomains allows one to cr eate all sorts of defect structures. The Fourier-transform segment of the program allows one to calculate neutron as well as X-ray intensiti es including isotropic temperature factors and anomalous scattering. T he 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 Fo rtran77 and the source code is available via the World Wide Web.