engleski

Lattice dynamics of semirigid molecules

A new approach to the lattice dynamics calculations for the crystals built up from semirigid molecules is presented. The rigid body approximation often used in the calculation of the lattice dynamics of molecular solid is extended to the molecules built from several rigid subunits (polyphenyles, etc.). The intermolecular force field is calculated from the atom– atom potential function. The intramolecular force field describing the dynamics of the rigid subunits within the molecule is calculated in the frame of the central force field model (CFF), i.e., assuming only the stretching coordinates between certain bonded and nonbonded atoms within the molecule. The parameters (force constants) are fitted in order to reproduce the observed low vibrational frequencies of the free molecule. The method is applied to the lattice dynamics of biphenyl, 2, 2-bipyridine and s-trans-bicyclopropyl. The possibility of the application of the present method in the calculation of Raman and coherent inelastic neutron scattering intensities is discussed.

lattice dynamics ; biphenyl ; 2 ; 2-bipyridine ; s-trans-bicyclopropyl ; rigid units ; low frequency vibrations ; phonons

nije evidentirano