Molecular dyunamics simulation of extreme thermal and mechanical conditions

这项提案中概述的目标有两个：首先，我们希望提高我们用原子模拟，特别是分子动力学对材料建模的能力。为此，我们希望提高我们预测分子体系静电学的能力，而不必回到第一原理方法。其次，我们计划调查特定的、技术上相关的材料对极端条件的反应。我们发现，由于我们无法预测分子体系的静电学，基于分子动力学的过程涉及配位变化或键断裂和形成的建模受到了强烈阻碍。我们希望进一步制定一项最近提出的计划，试图克服这一缺陷。新的方法结合了以前相互排斥的两种方案，具体地说，是静电学的键型描述和原子型描述。我们的方法开发还将支持在平等的基础上处理极化和色散相互作用的尝试。MD的更广泛的应用预计将用于两类材料，特别是用作润滑剂抗磨添加剂的金属磷酸盐，以及用于光学存储介质的所谓相变材料，即由Ge、Sb和Te组成的合金。这两类材料的结合元素是，它们的功能似乎与配位变化密切相关，例如，锌在压力下改变其在锌盐中的配位(从而形成网状抗磨膜)，而锗在激光照射下改变其配位(从而在导电和绝缘之间切换)。为了更好地根据我们的需要定制这些材料，我们计划更彻底地了解它们的相图，特别是它们的详细化学成分。希望为高密度光存储介质和新型环保抗磨添加剂的设计提供指导。

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.