CRUSH: the rigid unit mode program

CRUSH is a program designed to probe and analyze the origin of displacive phase transitions in crystal structures that can be described as frameworks or networks of connected polyhedra. Examples are aluminosilicate minerals and zeolites. The displacive phase transitions involve low frequency phonons “Rigid Unit Modes” which, to first order, will require no distortions of the structural polyhedra moving as if they are rigid units. The RUM model can be applied to a range of problems that include understanding the nature of hightemperature phases, understanding the origin of negative thermal expansion, predicting localized distortions in zeolite structures, and identifying the flexibility of network glasses. Further information is available at http://www.esc.cam.ac.uk/rums.