UBC Theses and Dissertations

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UBC Theses and Dissertations

Computational studies on functional materials Chen, Yuzhe


Carbon nanotubes (CNTs) are of great significance due to their almost unlimited potential applications. Transition metal doped CNTs in particular can be developed into small molecule sensors or CNT based catalysis and theoretical studies are important methods to predict their structures and properties. The Project I of this thesis focused on the development of a model that is specifically used for the study of transition metal doped single wall CNT (SWCNT) systems at a reduced computational cost for neutrally charged systems. Longer SWCNT segments of about 20 layers of carbon and terminated by hydrogen or nitrogen atoms with single transition metals doped in exo and endo modes as well as the transition state of the exo-endo transformation were utilized to benchmark our new model. Numerical results show that the new model with a shorter length of SWCNT segment is able to accurately represent geometrical and electronic structures of longer ones based on conventional termination schemes. Computational results further indicate that the transition barrier heights between the exo and endo modes of various metal-doped systems are ranging from 0.1 to 5 eV. Further research work include the study of other elements or metal clusters as dopants, the ionized version of our doped SWCNT systems, as well as to test with other functional methods. Finding the weakest bond within a molecule is crucial for understanding the mechanisms behind chemical reactions and the bond dissociation energy (BDE) is used frequently for locating the weakest bond. However, it requires one to perform tedious calculations of BDEs for all bonds within a molecule. To save time and computational resources, we made attempts to design reasonable yet simple structural indicators to identify weak chemical bonds in Project II. Based on the commonly available structural property indicators for bond strength, such as bond length, the Mulliken interatomic electron number, and the Wiberg bond order, we have created several new bond-strength indicators that can be directly used to efficiently identify almost all weak bonds. In the future, different chemical systems will be analyzed by the new indicators to test their reliabilities.

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