LATTICE-DYNAMICS OF THE ORTHORHOMBIC PHASE OF KCLO4 - EWALD METHOD IN MOLECULAR COORDINATES

The algorithm of the Ewald lattice sums is formulated in a form suited for application to lattice dynamics calculations for ionic molecular crystals, employing molecular coordinates and a discrete-charges representation of the Coulomb interactions. The method is used for a lattice dynamics calculation of KClO4 crystal, including external and internal degrees of freedom. An atom/atom plus charge/charge potential is used, providing a remarkably good agreement with the experimental data. The calculation is extended also to the anharmonic properties: the calculated linewidths of the external phonons compare satisfactorily to the observed values.