ITR: Science and Software for Predictive Simulation of Chemo-Mechanical Phenomena in Real Materials

这个奖项是为了响应提交给2003财年信息技术研究（ITR）招标的中型提案。 它由材料研究部和化学部共同支持。 除了在佛罗里达进行的初步研究外，麻省理工学院和亚利桑那州也将进行研究。这项分子模拟研究的主要特点是：它是基于量子力学的;预测性的;化学精确的;以及电子态特异性的。 最初的重点将是水对二氧化硅纳米棒的性质和纳米结构中的电子传输的影响。 材料的计算机建模并不比用来描述原子间相互作用的力更好。 这些通常基于经典物理学，允许快速生成大规模模拟所需的力。 但是，由于键断裂和形成，光学性质和化学反应的经典描述很差，可靠的建模最终必须基于量子力学（QM）。 但是量子计算是计算密集型的，这导致了一种多尺度方法，在这种方法中，量子力学被用于关键区域，然后嵌入经典模拟中。 为了使材料模型具有足够的预测性来指导实验，量子力学的引入是必要的。模拟必须具有化学准确性，这是一个必要的特征，如果建模要成功解决长期未解决的问题，例如为什么二氧化硅在潮湿时比干燥时弱几个数量级，而向二氧化硅中加入氨却没有这种效果。 一个适当的，基于量子力学的模拟应该反映这些差异，定性和定量。 另一个主题是，通过在模拟中使用QM，实现电子状态特异性。 经典模型不区分基态和激发态，在本研究的前期工作中提出的转移哈密顿量（TH）具有一种函数形式，它允许简化的量子力学在提高计算速度的同时保持预测质量，并且是常用紧束缚（TB）近似的推广，它克服了TB不能描述键断裂的缺陷。 TH与流行的密度泛函理论方法的不同之处在于，它适合于真正的QM哈密顿量，而不是密度或能量。 量子区域之间的界面和它们的经典嵌入将使用密度算子Liouville-von Neumann动力学进行量化，该动力学提供了一个框架，用于将完全QM系统分为两个部分，以经典或介电方式建模。该项目的关键成果将是化学精确和现实材料建模的新理论方法，以及应用于挑战性问题的软件实现。 大量的研究生和博士后助理将得到支持，以及本科生，重点是代表性不足的群体。 关于材料模拟结果的会议将纳入年度Sanibel会议。 所产生的软件将通过伊利诺伊大学的材料计算中心提供给更广泛的社区。该奖项是对提交给2003财年信息技术研究（ITR）征集的中型提案的回应。 它由材料研究部和化学部共同支持。 除了在佛罗里达进行的初步研究外，麻省理工学院和亚利桑那州也将进行研究。这项分子模拟研究的主要特点是：它是基于量子力学的;预测性的;化学准确的;以及电子态特异性的。 最初的重点将是水对二氧化硅纳米棒的性质和纳米结构中的电子传输的影响。 该项目的主要成果将是用于化学精确和现实材料建模的新理论方法，以及应用于具有挑战性问题的软件实现。 大量的研究生和博士后助理将得到支持，以及本科生，重点是代表性不足的群体。 关于材料模拟结果的会议将纳入年度Sanibel会议。 所生产的软件将通过伊利诺伊大学的材料计算中心提供给更广泛的社区。

This award is in response to a medium proposal submitted to the FY03 Information Technology Research (ITR) Solicitation. It is jointly supported by the Division of Materials Research and the Chemistry Division. In addition to primary research at Florida, research will also be done at MIT and Arizona.Themes that distinguish this research on molecular simulations are that it is quantum mechanically based; predictive; chemically accurate; and, electronic state specific. The initial focus will be on the effect of water on the properties of a silica nanorod and on electron transport in nanostructures. Computer modeling of materials can be no better than the forces used to describe the interaction among the atoms involved. These are usually based on classical physics, which permits the rapid generation of forces required for large-scale simulations. But because bond breaking and formation, optical properties, and chemical reactions are poorly described classically, reliable modeling must ultimately be based on quantum mechanics (QM). But quantum calculations are computationally intensive, leading to a multi-scale approach in which quantum mechanics is used in critical regions, which are then embedded in a classical simulation. The inclusion of quantum mechanics is necessary to make materials modeling predictive enough to guide experiment.Simulations must be chemically accurate, a necessary feature if modeling is to succeed on long unsolved problems such as the reason why silica, when wet, is weaker by several orders of magnitude than when dry, while addition of ammonia to silica shows no such effect. A proper, quantum mechanically based simulation should reflect these differences, qualitatively and quantitatively. Another theme is that, by using QM in the simulations, electron state specificity is achieved. Classical models do not distinguish between ground and excited electronic states.A transfer Hamiltonian (TH), developed in work preparatory to this research, has a functional form that permits simplified QM to retain predictive quality at increased computation speed, and is a generalization of the frequently used tight-binding (TB) approximation that cures TB's inability to describe bond breaking. The TH differs from the popular density functional theory methods in that it fits to the true QM Hamiltonian rather than to densities or energies. The interface between quantum regions and their classical embedding will be quantified using a density-operator Liouville-von Neumann dynamics that offers a framework for separating a fully QM system into two parts, modeling one in a classical or dielectric manner.The key results of the project will be new theoretical methods for chemically accurate and realistic materials modeling, and their software implementation, applied to challenging problems. A large number of graduate students and postdoctoral associates will be supported, as well as undergraduate students with an emphasis on underrepresented groups. Sessions on materials simulation results will be integrated into the annual Sanibel meetings. Software produced will be made available to the wider community through the Materials Computation Center at the University of Illinois.This award is in response to a medium proposal submitted to the FY03 Information Technology Research (ITR) Solicitation. It is jointly supported by the Division of Materials Research and the Chemistry Division. In addition to primary research at Florida, research will also be done at MIT and Arizona.Themes that distinguish this research on molecular simulations are that it is quantum mechanically based; predictive; chemically accurate; and, electronic state specific. The initial focus will be on the effect of water on the properties of a silica nanorod and on electron transport in nanostructures. The key results of the project will be new theoretical methods for chemically accurate and realistic materials modeling, and their software implementation, applied to challenging problems. A large number of graduate students and postdoctoral associates will be supported, as well as undergraduate students with an emphasis on underrepresented groups. Sessions on materials simulation results will be integrated into the annual Sanibel meetings. Software produced will be made available to the wider community through the Materials Computation Center at the University of Illinois.