Condensed Matter - Theory

艾伦9725037这是一个更新奖进行理论研究的金属，或近金属，氧化物和玻璃。 玻璃态固体中热振动的简正模已经在计算机上对多达4096个原子进行了研究。 这些模型产生了非晶硅的真实振动。 计划开展四个新项目：（1）阐明简正模扩散率的概念;（2）找到低能“共振“模和与共振模强耦合的低能结构重排之间的联系;（3）发展热振动粘性理论并将其应用于玻璃内摩擦的研究;（4）发展了定域态集中时热传导的跳跃理论。 虽然大多数重要的氧化物是绝缘的，但有些是非常好的金属，最有趣的是在边界上。 从金属到绝缘的转变通常有两个同样强大但非常不同的驱动力，库仑相关和晶格畸变。 前者即使在最简单的完全相互作用模型中也会引起很大的理论困难，而后者原则上是可解的，根据化学物种和晶体结构有多种表现形式。 目前正在完成对库仑效应最小的BaBiO 3的研究。 为了提取许多氧化物的共同物理，使用了Rice和Sneddon的简化模型，其中唯一的晶格自由度是氧原子平行于金属-氧键的位移。 这不仅捕获了驱动Bi（3+）/Bi（5+）反离子化（并引起绝缘行为）的呼吸畸变，而且捕获了与Eg金属和T2 g金属以及许多等电子材料的金属-绝缘体行为耦合的Jahn-Teller位移原理。 这项理论研究将继续研究金属氧化物材料及其不寻常的性质。 这些材料因其各种各样的性质而令人感兴趣。 有些像普通金属一样导电，而另一些则绝缘。 有些介于金属特性和绝缘特性之间。 这项资助支持的研究将调查这类困难但技术上重要的材料。 ***

Allen 9725037 This is a renewal award to conduct theoretical research on metallic, or nearly metallic, oxides and on glasses. The normal modes of thermal vibration in glassy solids have been characterized in computer studies of up to 4096 atoms. These models yield realistic vibrations for amorphous silicon. Four new projects are planned: (1) Clarify the concept of diffusivity of normal modes; (2) Find connections between low energy "resonant"modes and low energy structural rearrangements which couple strongly to the resonant modes; (3) Develop a theory of the viscosity of the thermal vibrations and apply this to the study of internal friction in glasses; (4) Develop a new theory of hopping conduction of heat when localized states are concentrated. Although most important oxides are insulating, some are very good metals and the most interesting ones are on the borderline. The transition from metallic to insulating has usually two equally strong and very different driving forces, Coulomb correlation and lattice distortion. The former causes great theoretical difficulty even in the simplest fully interacting model, whereas the latter, solvable in principle, has multiple manifestations depending on the chemical species and crystal structure. A study of BaBiO3, where Coulomb effects are minimal, is currently being completed. To extract the common physics of many oxides, a simplified model due to Rice and Sneddon is used, where the only lattice degrees of freedom is the displacement of oxygen atoms parallel to the metal-oxygen bond. This not only captures the breathing distortion that drives the Bi(3+)/Bi(5+) disproportionation (and causes insulating behavior), but also captures the principle Jahn- Teller displacement which couples to the metal-insulator behavior of Eg metals and T2g metals and many isoelectronic materials. %%% This theoretical research will continue studies of metal oxide materials and their unusual properties. These materials are intr iguing due to their widely varied properties. Some conduct electricity, like normal metals, while others are insulating. Some are on the borderline between metallic properties and insulating properties. The research supported by this grant will investigate this difficult, but technologically important class of materials. ***