USING THE PHONON PROGRAM FOR INTERPRETING INELASTIC NEUTRON-SCATTERING DATA

The PHONON program was developed into a generally useful form for latt ice dynamic calculations using the quasi-harmonic approximation and ma de available to other users interested in the interpretation of INS da ta. By diagonalizing the dynamical matrix, the actual values of the om ega(q) for each wave vector q are determined. The dispersion curves ca n, therefore, be obtained and plotted using NAG graphic routines on a suitable computer. The weighted phonon density of states can also be o btained 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-rang e repulsive parts of the potential. Ionic polarisation is modelled usi ng the shell model. There are also a number of many-body potentials fo r molecular systems and lattice structures. These include angle bendin g three-body potentials and four-body (torsional) potentials.