Structure and Electronic Anomalies of Amorphous Chalcogenides

休斯敦大学的Vassiliy Lubchenko获得了化学学部化学理论、模型和计算方法项目的奖励，他开发了一种理论和计算方法来研究一类重要的无机固体，称为“硫族化合物”，它包含了XVI族（硫、硒、碲）、XV族（磷、砷、锑、铋）和XIV族（锗）的元素。这些固体易于在有序晶体和非晶态（“玻璃”）形式之间切换的能力允许人们以有效的方式调整这些材料的光学和电子特性。这一特性使硫族化合物成为光学驱动器、下一代计算机存储器和显示器、智能光学和新型计算机体系结构应用的主要候选者。非晶硫族化合物是一种特殊类型的无序固体，称为“玻璃”。硫系合金通常是通过将液体迅速冷却，使其低于其熔点而制成的。人们可以先将材料熔化，然后以特定的速度冷却，使硫系合金在玻璃和有序结晶形态之间转换。缓慢冷却生成晶体，快速冷却生成玻璃。本研究建立了硫族合金中玻璃化转变和量子化学相互作用的分子运动之间的详细联系。玻璃化转变的直接分子建模是困难的，并且是预测复杂无机固体结构和设计具有定制性能的材料的更大挑战的一部分。这项研究正在利用硫属化合物中不同化学相互作用之间相互作用的相似性，以及一个定义良好的数学物理模型的行为，以使问题易于处理。在更广泛的影响活动的中心是培训研究生，本科生，特别是高中生。一项策略是确保参与的高中生和本科生完成有意义的子项目，这些子项目将为同行评审的出版物做出贡献。该研究的微观假设是，硫族合金的玻璃形成能力源于不同类型化学键之间的竞争：共价键、多中心键和次生键。由此产生的复杂的相互作用被统计物理的经典模型所捕获，即正在实现的64顶点模型。计算的最重要的输出是无定形硫族化合物的结构和构型熵。构形熵决定了合金自由能结构的复杂性及其非晶成形能力。为了支持这些计算，一种新的程序正在实施，用于产生具有典型硫属化合物的扭曲八面体键的粒子的致密玻璃结构。基于结构简并固体弹性理论的六组分自旋模型是一种附加的粗粒化描述。

Vassiliy Lubchenko of the University of Houston is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry division to develop a theoretical and computational approach to studying an important class of inorganic solids, called the "chalcogenides," that contain elements from groups XVI (sulfur, selenium, tellurium), XV (phosphorus, arsenic, antimony, bismuth), and XIV (germanium). The ability of these solids to switch readily between ordered crystalline and amorphous ("glassy") forms allows one to tune the optical and electronic properties of these materials in an efficient way. This property makes the chalcogenides prime candidates for applications in optical drives, next generation computer memory and displays, smart optics, and novel computer architectures Amorphous chalcogenides are a special type of disordered solids called "glasses," which are ordinarily made by rapidly cooling a liquid, usually below its melting point One can convert a chalcogenide alloy between the glass and ordered crystalline form by first melting the material and, then, cooling the melt at a specified rate. Slow cooling yields the crystal, fast cooling yields the glass. The present study is establishing detailed connections between the molecular motions underlying the glass transition and quantum-chemical interactions in the chalcogenide alloys. Direct molecular modeling of the glass transition is difficult and is part of the greater challenge of predicting the structure of complex inorganic solids and designing materials with tailored properties. The study is exploiting the similarity of the interplay between distinct chemical interactions in the chalcogenides and the behavior of a well-defined model of mathematical physics to make the problem tractable. At the center of the broader impact activities is training of graduate, undergraduate, and, in particular, high school students. A strategy is in place to ensure the participating high school and undergraduate students complete meaningful subprojects that will contribute to peer-reviewed publications.The microscopic hypothesis of the proposed work is that the glass-forming ability of the chalcogenide alloys stems from a competition between distinct types of chemical bonding: covalent, multicenter, and secondary. The resulting complex interplay of interactions is captured by a classic model of statistical physics, viz., the 64-vertex model, which is being implemented. The most important outputs of the calculation are the structure and the configurational entropy of amorphous chalcogenides. The configurational entropy determines the complexity of the free energy landscape of the alloys and their glass-forming ability. To back up these calculations, a novel procedure is being implemented for generating dense glassy structures for particles with distorted-octahedral bonding typical of the chalcogenides. An additional coarse-graining description is being implemented with the help of a recently developed 6-component spin model based on the theory of elasticity of structurally-degenerate solids.