Molecular dynamics and anharmonic effects in the phonon spectra of solid carbon dioxide

Abstract

Anharmonic lattice dynamics (LD) and molecular dynamics (MD) calculations have been performed for solid CO 2 with two different intermolecular potentials. The IR and Raman spectra of the external phonons have been calculated from the MD simulation in the temperature range 25–150 K. The two potential models are shown to be characterized by a different degree of anharmonicity: very broad bands are obtained with the MOSMD potential, while the PRC-1 potential gives narrower spectral lines, in much better agreement with the experimental data. The anharmonic LD calculations agree with the MD results concerning the lineshape; LD instead predicts much larger positive shifts of the phonon frequencies. Such a discrepancy is attributed to the approximation implicit in the perturbative method utilized in LD.