PNNL

Abstract

Calculations of processes that depend on electronic states or charge transfer in bulk glasses are challenging because of the limitations imposed by the need to use ab initio methods. Cluster-based calculations alone cannot capture the response of the network structure that occurs upon bond rupturing or other alteration of the local molecular framework. From the atomic level perspective, it is necessary that simulations of extended (bulk) amorphous systems sample a large number of possible geometrical arrangements of molecular structures as well as their frequency and relative spatial distribution. To acheive this in sample sizes amenable to ab initio methods, we create multiple controlled samples, that as an ensemble provide a good statistical sampling of the bulk structure. In this work, glass samples are first generated using classical molecular dynamics then transferred to ab initio molecular dynamics where the samples are optimized using density functional theory. The optimal structures obtained by classical molecular dynamics (MD) and ab initio MD methods are compared to each other and to the classical simulation of a larger system.