Molecular dyunamics simulation of extreme thermal and mechanical conditions

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The goal outlined in this proposal is two-fold: First, we would like to increase our ability to model materials with atomistic simulations, in particular with molecular dynamics. For this purpose, we would like to improve our capability to predict the electrostatics of molecular systems without having to revert to first principle methods. Second, we plan to investigate the response of specific, technologically relevant materials to extreme conditions.     The molecular dynamics-based modeling of processes involving coordination changes or bond breaking and formation is strongly impeded by our inability to predict the electrostatics of molecular systems. We would like to further develop a recently suggested scheme that attempts to overcome this deficiency. The new approach combines two schemes that previously were mutually exclusive, specifically a bond-type and an atom-type description of electrostatics. Our method development will also support attempts to treat polarizability and dispersive interactions on an equal footing.     Applications of MD are anticipated for two classes of materials, specifically metal phosphates, which are used as anti-wear additives in lubricants, as well as so-called phase change materials, i.e., alloys consisting of germanium, antimony, and tellurium, which are used in optical storage media. The combining element of both classes of materials is that their functionality appears to be intimately linked to coordination changes, e.g., zinc changes its coordination in zincphosphates under pressure (thereby forming networked anti-wear films) and germanium changes its coordination under laser radiation (thereby switching the alloy between being conducting and being insulating). To be better able to tailor these materials to our needs, we plan to obtain a more thorough understanding of their phase diagrams, in particular as a function of their detailed chemical composition. We hope to provide guidelines for the design of higher density optical storage media and new, environmentally friendly anti-wear additives.