Harmonic Dynamics of Anthracene Crystal

Abstract

A method is suggested for the calculation of the complete phonon spectrum of a polyatomic molecular crystal in the entire Brillouin zone. The spectrum includes both external and internal phonons and the method involves breaking up the high order dynamical matrix into several blocks covering large groups of phonons revealing marked intermode mixing inside a group and neghgible mixing among the modes of the neighbouring groups. The phonon mode structure is assigned through the analysis of the eigenvector matrix. The calculations using the suggested method are controlled by the calculation of all 144 frequencies at the point q = 0. The dispersion curves and the density of states of the entire 144-mode phonon spectrum of anthracene-d ₀ crystal are presented.