Design Of Novel Molecular Devices--A First-Principles Study

Aiming at utilizing molecules to perform information processing with low costs and high performance, the field of molecular electronics has attracted growing interests. With the advancement of the research methods and measurement techniques, various molecular devices have been made and provided many unique and useful properties. For instance, molecular switches and molecular wires serve as the most basic elements for a electric circuit, molecular rectifiers fulfils rectification function with low energy cost, molecular motors convert chemical energy to driving force, molecular memories store and process information at the atomic scale. These devices are not only small in size, but also possess unique physical and chemical properties which are not available in traditional devices.The rapid development in molecular electronics experimental research has brought both opportunities and challenges to theoretical study. The goals of the theoretical study are to explain experimental phenomena, reveal underlying mechanisms, and conduct effective and rational molecular design to guide the experiments. In this work, we combined the quantum chemistry calculation of molecular properties with the solid state physics description of device electrodes, to investigate the charge transport behavior in two novel molecular devices we designed. The main contents are as follows:The first chapter presents the fundamental principles of molecular electronics, including a brief introduction of its origin, the development in experimental and theoretical research, as well as a short introduction of several important types of molecular devices.In the second chapter, we introduces the quantum chemistry based method for molecular electronics, including the primary formula based on elastic scattering theory and Green’s function theory, the calculation of electron transmission probability, the expression of tunneling current, the description of the electric field effect, and the QCME (Quantum Chemistry for Molecular Electronics) software package we developed for the simulation of electron transport in molecular devices.In the third chapter, we have utilized the particular electrical properties of single walled carbon nanotubes (SWCNT) and a molecular container structure of cucurbituril to design a novel molecular electronics component. We have examined the charge transport behavior, based on which we explored the distribution of electronic wavefunction in various SWCNTs by varying the contact position of cucurbiuril. These would provide important information for the design, fabrication and utilization of molecular devices in experiments.In the last chapter, we designed an unique molecular wire which consists of periodic units of a multidecker bis(benzene)chromium sandwich linked to a fullerene. The unique electronic and geometric structures of the-(arene-chromium-arene)-fullerene-complex unit were modeled by the quantum chemistry program Gaussian09.The QCME software package was employed to simulate and analyze the charge transport ability. By applying bias voltage on the molecular wire from different directions, we have examined the manipulation of electron transport by gate bias control, and demonstrated it as a promising component for future quantum computing applications.