Calculation of dispersion relations and frequency distribution of crystalline benzene

The dispersion relations for crystalline benzene at 138°K have been calculated using semiempirical atom-atom potential functions, for many relevant directions of the k vector in the Brillouin zone. The importance of mixing between lattice and low-lying internal vibrations is investigated. The semiempirical atom-atom potential functions have been employed for calculating the density of state according to the interpolation method of Gilat and Raubenheimer [Phys. Rev. 144, 390 (1966)].