Molecular Quantum-Dot Cellular Automata - Electronic Structure, Dynamics, Structure-Functionality Relation, and Self-Doping

The quantum-dot cellular (QCA) paradigm is an alternative approach to implement nanoelectronics. The binary information is encoded in the charge configuration within a cell comprised of several dots. There is no current flow between QCA cells, instead the Coulomb interaction between cells enables computation, thus avoid high power dissipation. QCA can be realized at the molecular scale, at which each cell is given by a single molecule and quantum dots are provided by redox centers.This thesis focuses on the theoretical study of molecular QCA. Two recent synthesized candidate molecules have been studied by quantum chemistry ab initio calculations. The bistable charge configurations of the molecules are identified, and the Coulomb interactions between neighboring molecules are analyzed, demonstrating that the interactions between molecules are sufficient to enable room temperature operation. A theoretical model is developed to characterize the bistability of molecular QCA. This model connects the QCA bistability to molecular structure. It is determined that the bistability of QCA molecules can be characterized by two structural parameters of molecules. This model is in good agreement with high-level ab initio techniques. Also, the dynamics of QCA devices is studied with coherence vector formalism. A model Hamiltonian for each QCA cell is constructed based on first-principle calculations, and coherent vector formalism is applied to calculate the switching dynamics of QCA circuits, including switching speed, clocking frequency, energy dissipation, and the structure-functionality relation of molecular QCA. Finally, a self-doping mechanism for molecular QCA is discussed. Boron clusters are analyzed as feasible dopants that could create mobile charges in the molecular cell. This mechanism keeps the whole molecular system neutral, thus avoids the effects of counterions that could otherwise hinder the information flow of a QCA array.