Molecular Dynamics Glass Simulation and Equilibration Techniques

To determine the effect of molecular dynamics simulation methodology on both the structural and dynamic properties of fluoride glasses, a large number of simulations were carried out using the same simulation box, potential, initial starting point and final temperature. It has been shown that the simulation methodology is, at least, as important as the potential in determining the final glass structure. Two useful tools have been developed which can, with more accuracy than present techniques, determine the point of homogeneity or equilibrium in glass simulations. These are a spherical average of all ions and a spherical average of each ion type within a sphere of radius half a box length. It has also been shown that, for a constant volume simulation, the use of the canonical ensemble (NVT) can lead to a structure that is not in its minimum potential energy configuration. Therefore, a combination of the canonical (NVT) and microcanonical (NVE) ensembles were used. Finally, a methodology is suggested that appears optimal for molecular dynamics glass simulations of the type performed in this paper.