First-Principles Studies of Raman-Active Modes in IV-VI Chalcogenide Glasses

本研究将利用第一性原理、密度泛函理论聚类计算来研究IV-VI硫系玻璃GexSe1-x和SixSe1-x的拉曼活性模式。这些材料的拉曼光谱显示出玻璃的刚性转变作为x的函数的明显迹象。计算的目的是将观察到的拉曼光谱特征的变化与潜在原子结构的相应变化联系起来。这样，计算将导致对这些材料的刚度转变和中短范围顺序的更详细的理解。本研究项目将以系统研究玻璃的簇模型为特色。每个簇将包含一个或多个玻璃的基本结构单元。每个星团的振动模式将使用标准方法计算，然后这些模式的绝对拉曼光谱强度将使用一种新的基于dft的技术从第一原理计算。计算将产生预测的拉曼光谱，可以直接与实验结果进行比较。比较将有助于确定负责特征光谱特征的短距离阶。此外，计算的绝对拉曼强度可用于预测玻璃中基本结构单元的相对浓度。这是一个全新的功能，将在本项目中首次使用。浓度信息对于许多关于玻璃结构的问题和刚度转变的重要细节都是至关重要的。本项目包括本科生和硕士生。这是一个芮奖，用于支持玻璃半导体性质的理论研究。本科生和硕士生都将参加。

9972333JacksonIn this Research at Undergraduate Institutions (RUI) grant, first-principles, density functional theory cluster calculations will be used to study the Raman-active modes of IV-VI chalcogenide glasses GexSe1-x and SixSe1-x . The Raman spectra of these materials exhibit clear signs of the rigidity transition predicted for glasses as a function of x. The object of the calculations is to link the observed changes in the Raman spectral features to corresponding changes in the underlying atomic structure. In this way the calculations will lead to a more detailed understanding of the rigidity transition and of the short and intermediate range order in these materials. This research project will feature systematic studies of cluster models of the glasses. The clusters will each contain one or more of the basic structural units of the glass. The vibrational modes of each cluster will be computed using standard methods and then the absolute Raman spectral intensities for these modes will be computed from first-principles using a new DFT-based technique. The calculations will produce predicted Raman spectra that can be compared directly to experimental results. The comparisons will serve to identify the short-rang order responsible for the characteristic spectral features. In addition, the calculated absolute Raman intensities can be used to predict the relative concentrations of basic structural units in the glass. This is an entirely new capability that will b used for the first time in this project. The concentration information is fundamental to many questions regarding the structure of the glasses and to important details of the rigidity transition. Both undergraduates and masters students will participate in this project. This is an RUI award to support theoretical research on the properties of glassy semiconductors. Both undergraduate students and masters students will participate.