Using the PHONON program for interpreting inelastic neutron scattering data

The PHONON program was developed into a generally useful form for lattice dynamic calculations using the quasi-harmonic approximation and made available to other users interested in the interpretation of INS data. By diagonalizing the dynamical matrix, the actual values of the ω(q) for each wave vector q are determined. The dispersion curves can, therefore, be obtained and plotted using NAG graphic routines on a suitable computer. The weighted phonon density of states can also be obtained by integration over all the possible values of q lying in the first Brillouin zone of the crystal. There is a wide range of two-body potentials programmed into the code which are used for the short-range repulsive parts of the potential. Ionic polarisation is modelled using the shell model. There are also a number of many-body potentials for molecular systems and lattice structures. These include angle bending three-body potentials and four-body (torsional) potentials.