Large Scale Simulations and Local Analysis of Si-based Materials to Study their Energetics, Bonding, and Structural Properties

这是一个理论研究项目，主要是计算性的，涉及路易斯维尔大学和橡树岭国家实验室。还有与威斯康辛大学的实验性合作。主要目标是基于有序O(N)非正交紧密结合分子动力学（NOTB-MD）进行大规模模拟，以准确预测si基材料的结构、电子和键合性能。最近，两位PI在nob哈密顿量的背景下开发了一种用于计算总能量和原子力的O(N)技术。O(N)技术的重要性在于，它克服了传统总能量和原子力计算中存在的瓶颈，将计算时间从N3减少到N，其中N表示系统的大小。NOTB哈密顿量的优点是它包含了电子结构的量子力学描述，它最适合于在MD模拟中遇到任意协调的情况。因此，O(N) NOTB-MD方案提供了一种极好的方法来研究具有现实尺寸的系统，这些系统目前超出了第一性原理分子动力学模拟的范围。此外，利用创新的局部测度和真实空间格林函数方法，结合O(N) NOTB-MD技术，现在有了一个强大的工具来分析从MD模拟中获得的大量信息。进行大规模模拟和在微观水平上准确预测性质的双重主题是本研究的独特特征之一。这项研究由四个项目组成。第一个重点是Si（100）表面上Si和Ge沉积生长的初始阶段。第二部分是研究沉积在Si（001）衬底上的Gen薄膜从二维到三维生长过渡的开始。在项目三中，将研究从几百到几千个原子的硅纳米粒子的平衡和电子结构，目的是了解量子限制对这些纳米系统性质的影响。最后，项目四着眼于与纳米异质结构（SixGe1-x）的制造有关的问题，并将探讨应变对其性能的影响。本研究的科学成果有望导致对Si（100）衬底上Si和Ge沉积中单体的吸附与生长结构形成之间的联系，岛屿的形成，合金的有序和表面偏析，纳米颗粒的平衡形状，量子限制对Si纳米颗粒性能的影响等的理解。%%%涉及路易斯维尔大学和橡树岭国家实验室。还有与威斯康辛大学的实验性合作。中心目标是进行大规模模拟，以准确预测硅基材料的结构、电子和键合特性。进行大规模模拟和在微观水平上准确预测性质的双重主题是本研究的独特特征之一。本研究的科学成果将有助于理解硅衬底上硅和锗沉积中单体的吸附与生长结构形成之间的联系、岛屿的形成、合金的有序和表面偏析、纳米粒子的平衡形状、量子约束对纳米硅性能的影响等。研究成果将具有重大的基础意义，并将在微电子工业中得到广泛的应用。＊＊＊

9802274 Jayanthi This is a theoretical research project, largely computational, involving the University of Louisville and Oak Ridge National Laboratory. There is also experimental collaboration with the University of Wisconsin. The central objective is to perform large scale simulations based on the order-N O(N) non-orthogonal tight-binding molecular dynamics (NOTB-MD) to predict accurately the structural, electronic, and bonding properties of Si-based materials. Very recently an O(N) technique for the calculation of both total energy as well as atomic forces has been developed by two of the PI's in the context of a NOTB Hamiltonian. The importance of the O(N) technique is that it overcomes the bottleneck present in the conventional total energy and atomic force calculations by reducing the scaling of computational time from N3 to N, where N denotes the size of the system. The advantage of NOTB Hamiltonian is that it incorporates a quantum mechanical description of the electronic structure and it is best suited for situations with arbitrary coordination encountered in MD simulations. Hence, the O(N) NOTB-MD scheme provides an excellent means to investigate systems with realistic sizes that are currently outside the scope of first-principles molecular dynamics simulations. Furthermore, using innovative local measures and the method of real space Green's function in conjunction with the O(N) NOTB-MD technique, a powerful tool is now in place to analyze the vast amount of information obtained from a MD simulation. The twin theme of performing large scale simulations, and predicting properties accurately at the microscopic level, is one of the unique features of this research. The research is comprised of four projects. The first focuses on the initial stages of growth of Si and Ge depositions on a Si(100) surface. The second is concerned with the study of the onset of the transition from a two- dimensional to three-dimensional growth for Gen films d eposited on the Si(001) substrate. In project three, equilibrium and electronic structures of Si nanoparticles from a few hundred to a few thousand atoms will be investigated with the aim of understanding the effect of quantum confinement on the properties of these nanosystems. Finally, project four looks at issues related to the fabrication of nanoheterostructures (SixGe1-x) and the effect of strain on their properties will be explored. The scientific outcome of this study is expected to lead to the understanding of the link between the adsorption of monomers and the formation of growth structures in Si and Ge depositions on the Si(100) substrate, the formation of islands, alloy ordering and surface segregation, equilibrium shape of nanoparticles, the effect of quantum confinement on the properties of Si nanoparticles, etc. %%% This is a theoretical research project, largely computational, involving the University of Louisville and Oak Ridge National Laboratory. There is also experimental collaboration with the University of Wisconsin. The central objective is to perform large scale simulations to predict accurately the structural, electronic, and bonding properties of silicon-based materials. The twin theme of performing large scale simulations, and predicting properties accurately at the microscopic level, is one of the unique features of this research. The scientific outcome of this study is expected to lead to the understanding of the link between the adsorption of monomers and the formation of growth structures in silicon and germanium depositions on the silicon substrate, the formation of islands, alloy ordering and surface segregation, equilibrium shape of nanoparticles, the effect of quantum confinement on the properties of silicon nanoparticles, etc. Research results will be of great fundamental interest and will find broad application in the microelectronic industry. ***