COMPUTATIONAL DETERMINATION OF THE ELASTIC PROPERTIES OF THE ALPHA-PHENAZINE CRYSTAL

Harmonic lattice dynamical calculations in the rigid-body approximatio n are employed to probe elastic and dynamic properties of the alpha-ph enazine molecular crystal. The intermolecular interaction for an optim ized lattice structure is defined by the Buckingham potential. The vel ocities of the acoustic phonons obtained from dispersion curves of nor mal modes in the region of the Brillouin zone center allow evaluation of the full set of elastic constants. Modeling of the homogeneous defo rmation of the crystal lattice is used to obtain frequency changes of the optic modes, which yield estimates for the anisotropic mode Grunei sen parameters. Relaxation of the internal strains is employed for a r ealistic modeling of the crystal response to the external strains and stresses. The anharmonicity and anisotropy of the intermolecular inter actions are assessed from the derived parameters.