Lattice-dynamical calculations on some rigid organic molecules

Several physical-chemical properties in crystals formed by "rigid" organic molecules have been calculated by means of different semiempirical atom-atom potential functions. For nine different substances, vibration frequencies, dispersion curves, and "crystallographic" temperature factors have been evaluated, and as an example the density of states for two of them are also reported. Experimental data are in excellent to fair agreement with results obtained by use of "Williams IVa" functions; some of these results can be advantageously used for libration correction of bond lengths that are determined by x-ray or neutron diffraction. Among the examined substances, some anomalies are found for pyrene crystals, which confirm in this case a rather unusual way of packing.