Electronic Structure Study of Metallized Carbon Clusters and Silicon Carbide Nanostructures




Patrick, Anthony D.

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Binary structures of carbon with lithium, beryllium, or silicon are predicted using density functional (DFT) methods in the case of the metallized clusters, or tight-binding (TB) methods in the case of the silicon carbide structures. Small carbon clusters metallized with Li or Be were studied within the hybrid density functional approach with a generalized gradient approximation (GGA) correction. Structures of the ground state and several excited states associated with different isomers and multiplicites were systematically calculated for CxLiy with x = 1-3 and y = 1-5 for carbon-lithium clusters and x = 1-3 and y = 1-4 for carbon-beryllium clusters. The most stable isomers are linear or planar in the ground state. There is charge transfer in these compounds, showing that ionic bonding is favored as the cluster grows in size. Ionization potentials, electron affinities, and vibrational analysis of all studied states of metallized clusters are provided. The thermal stability of the ground state isomers was verifi ed within the harmonic approximation of the Helmholtz free energy up to temperatures of about 1000 K. Structural transitions where detected for C2Li2, C2Li4, and C2Be3. A tight-binding parameterization for silicon carbide nanoclusters was developed based on the electronic energy of small clusters calculated within the GGA of DFT. This parameterization includes s and p angular momentum symmetries with a nonorthogonal atomic basis set such that the parameters enter in the on-site, hopping, and overlap TB Hamiltonian and overlap matrices. With the aid of these new parameters, the minima of silicon carbide nanoclusters, nanotubes, and nanowires, were predicted. Growth sequences and stability patterns along with the energetics, symmetry, structure, and band gaps are reported for all predicted structures.



Molecular clusters, Tight binding, Silicon carbide, Density functional theory, Metal carbides, Metallization