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

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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. ***