Structural correlations and phonon density of states inGeSe2: A molecular-dynamics study of molten and amorphous states

Abstract

With use of the molecular-dynamics technique, the structural and dynamical correlations in molten and vitreous ${\mathrm{GeSe}}_2$ are investigated with an effective interionic potential which consists of Coulomb, charge-dipole, and steric interactions. It is found that the short-range order is dominated by Ge(${\mathrm{Se}}_{1/2}$ ${)}_4$ tetrahedra and the Ge-Se, Se-Se, and Ge-Ge bond lengths are 2.35, 3.75, and 4.30 Å, respectively. The static-structure factor exhibits the first sharp diffraction peak (FSDP)–a characteristic of the intermediate-range order in binary chalcogenide glasses. Partial pair-distribution functions and the corresponding static-structure factors indicate that Ge correlations are responsible for the FSDP, which is in agreement with differential-anomalous-scattering experiments. In the vitreous state, the FSDP displays an anomalous variation with temperature in that its height increases while the other peaks decrease in height upon heating. All the other peaks observed in the structural measurements are also found present in the calculated static-structure factor. The peak positions and their relative heights in the liquid and glass compare favorably with experiments. The calculated phonon density of states in the glass shows peaks at 8.0, 10.8, 26.4, 34.4, and 37.2 meV, which are in good agreement with the positions of the main peaks in inelastic-neutron-scattering experiments. In addition, we find a companion line of the symmetric breathing mode $A_1$ (26.4 meV) at 27.8 meV. Raman-scattering experiments also find the companion line to be ∼1.5 meV higher than the $A_1$ mode. The calculated phonon density of states has weaker features at 12.6, 17.2, and 22.0 meV and they are also observed by inelastic-neutron-scattering and Raman-scattering experiments.