Using the PHONON program for interpreting inelastic neutron scattering data

Abstract

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.