Short and intermediate range order in amorphous GeSe2
By using first-principle molecular dynamics within density functional theory, we study the structural properties of amorphous GeSe2 at a temperature T of 300 K. For each property, a statistical average is obtained from six independent partial averages taken on temporal trajectories, each one lasting 12 ps. Each trajectory stems from an initial configuration of the liquid phase at T=1100 K and is generated by extensive annealing at T=300 K. Overall, our level of theory provides a picture of this prototypical disordered network-forming glass that is quantitatively consistent with neutron diffraction data. Very satisfactory agreement with experiments is obtained for the pair correlation functions g(GeSe)(r) and g(SeSe)(r) in terms of peak intensities and positions. This holds true also for the amount of Se-Se homopolar bonds and the Ge-Se and Se-Se coordination numbers. Conversely, the g(GeGe)(r) pair correlation function is much less structured around the main peak position and the concentration of Ge-Ge homopolar bonds is lower than in the experiment. The network organizes itself through the predominant presence of GeSe4 tetrahedra. However, other coordinations occur in non-negligible proportions for both Ge and Se. Total and partial structure factors reproduce very well the experimental patterns for wave numbers k larger than 2 A(-1). For smaller k values, the largest difference between theory and experiment is exhibited by the S-GeGe(k) structure factor, showing a FSDP of lower intensity in the simulation. In agreement with experimental results, a sizeable feature is found at the FSDP location in the Bhatia-Thornton concentration-concentration structure factor S-CC(k).