Calculations of Phonon Dynamics in Solid Biphenyl. Mixing Between Interphenyl and Lattice Vibrations

Abstract The calculation of the lattice dynamics in the high‐temperature phase of solid biphenyl is performed with the inclusion of low‐lying interphenyl motions. The quasi‐harmonic approximation is applied and use is made of the semiempirical atom—atom potential of the form „6‐exp”︁. On the basis of calculated phonon curves the effect of mixing between external and internal modes is studied. The frequencies of the phonons in the Brillouin zone centre are compared with optical spectroscopic results. The phonon density of states weighted on the hydrogen motions is compared with low‐temperature inelastic incoherent neutron scattering spectra. Comparison of the calculated and measured values shows good agreement.

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