Molecular dynamics study of linear diatomic chain

Abstract

The molecular dynamics method is applied to a linear system of 64 diatomic molecules with periodic boundary conditions. The molecules interact via the sum of harmonic and quadrupole potentials. A pseudo phase transition from hindered to rotational diffusion is found. Results are given for energy, specific heat, equation of state, order parameter, dynamical structure factor, angular velocity correlation function, and relaxation times. At low temperature the peaks in the dynamical structure factor can be identified with translational and torsional phonons. They generally agree with the predictions of harmonic lattice dynamics. At high temperatures the existence of large quasielastic peaks indicates on the rotational diffusion of molecules. The model is tested by both the classical and quantum pseudoharmonic approximations.