ELASTICITY, BULK MODULUS, AND MODE GRUNEISEN PARAMETERS OF THE HPTB MOLECULAR-CRYSTAL - COMPUTATIONAL INVESTIGATION OF A CLATHRATE PRECURSOR

Harmonic lattice dynamical calculations in the rigid-body approximatio n are employed to obtain frequencies of normal modes in the region of the Brillouin zone center for the hexakis(phenylthio)benzene (HPTB) mo lecular crystal. The intermolecular interaction for an appropriately o ptimized lattice structure is defined by the Buckingham potential with pertinent parameters. The velocities of the acoustic phonons are used to derive the full set of elastic constants and then the bulk modulus . Homogenous deformation of the crystal lattice provides frequency cha nges of the Raman active modes which allows calculation of selected an isotropic mode Gruneisen parameters. Relaxation of the internal strain is used for a realistic modeling of tire crystal response to the exte rnal strains and stresses. The anharmonicity and anisotropy of the int ermolecular interaction are assessed from the derived parameters.