"Design of new materials using computational nanoscience" - Over the past decade, first-principles-based computational nanoscience has emerged as a powerful tool for designing new material nanostructures with potential for a broad range of technological applications. In this area, my research group develops and implements atomic-scale and multi-scale computational modeling tools to study the synthesis and processing of nanostructured forms of electronic and photonic materials and to predict their structure, properties, and function. This presentation focuses on a fundamental understanding of structure-property relations in graphene-based carbon nanostructures and in ternary semiconductor quantum dots aiming at materials design for nanoelectronic and photovoltaic technologies, respectively. Based on a combination of first-principles density functional theory (DFT) and classical molecular-dynamics (MD) simulations, we have analyzed carbon nanostructure formation from twisted bilayer graphene, upon creation of interlayer covalent C-C
bonds due to patterned hydrogenation or fluorination. For small twist angles and twist angles near 30 degrees, interlayer covalent bonding generates superlattices of diamond-like nanocrystals and of caged fullerene-like configurations, respectively, embedded within the graphene layers. Computed electronic band structures of these superlattices show that their band gaps can be tuned through selective chemical functionalization and creation of interlayer bonds and range from a few meV to over 1.2 eV, which is promising for nanoelectronic applications. The mechanical properties of these superstructures also can be precisely tuned by controlling the fraction of sp3-hybridized C-C bonds in the material through the extent of chemical functionalization. In another area, following a hierarchical modeling approach that combines first-principles DFT calculations and classical Monte Carlo (MC) simulations with a continuum species transport model, we have predicted the atomic-species concentration profiles in ternary inorganic semiconductor quantum dots (QDs) during their thermal annealing and how such profiles affect the QDsÃ¢ÂÂ electronic band structures. The properly parameterized continuum model aids in the design of post-growth thermal annealing processes to establish thermodynamically stable compositional distributions for the optimal photofunction of ternary QDs grown through one-step colloidal synthesis techniques.