ELASTIC-CONSTANTS AND LATTICE-VIBRATIONS OF CO2 AND C6H6

Calculations of the elastic constants and lattice vibrations Of CO2 and C6H6 have been carried out, using the harmonic lattice dynamic procedures available in the THBREL and THBPHON programs. In addition to the usual Buckingham functions describing the non-bonded interactions, intramolecular potentials are also employed. Two sets of calculations were performed, the first for rigid molecules and the second for flexible molecular units, with a view to assessing the effect of molecular flexibility on the computed values of the elastic tensor components and lattice vibration frequencies. The results are also compared with those of previous studies, using methods in which the rigid-body contributions are clearly isolated, and with available experimental data.