A tight-binding model Hamiltonian is newly parametrized for silicon carbide based on fits to a database of energy points calculated within the density functional theory approach of the electronic energy surfaces of nanoclusters and the total energy of bulk 3C and 2H polytypes at different densities. This TB model includes s and p angular momentum symmetries with nonorthogonal atomic basis functions. With the aid of the new TB model, minima of silicon carbide cagelike clusters, nanotubes, ring-shaped ribbons, and nanowires are predicted. Energetics, structure, growth sequences, and stability patterns are reported for the nanoclusters and nanotubes. The band structure of SiC nanotubes and nanowires indicates that the band gap of the nanotubes ranges from 0.57 to 2.38 eV depending on the chirality, demonstrating that these nanotubes are semiconductors or insulators. One type of nanowire is metallic, another type is semiconductor, and the rest are insulators.

Small carbon clusters C, C2 and C3 metallized with beryllium were studied by first principles within the hybrid density functional approach with generalized gradient correction. Cluster isomer structures for the ground state and several excited states where systematically calculated for CxBey with x = 1–3 and y = 1–4 including the vibrational analysis of all states. Ionization potentials and electron affinities are calculated for the ground state cluster isomers. The thermal stability of the ground state isomers was verified within the harmonic approximation of the Helmholtz free energy up to temperatures of about 1000 K. Within the family of clusters studied, C2Be3 undergoes a solid-like structural transition at about 260 K changing from a planar structure at low temperatures to a linear isomer at high temperatures.

Submitted for the MAR07 Meeting of The American Physical Society Structure and Dynamics of Silicon Carbide Clusters: A TightBinding Adaptive Monte Carlo Application ANTHONY PATRICK, XIAO DONG, ESTELA BLAISTEN-BAROJAS, Computational Materials Science Center, George Mason University, Fairfax, VA 22030, THOMAS ALLISON, ANWAR HASMY, National Institute of Standards and Technology — A tight-binding parametrization for silicon carbide nanoclusters was developed based on the electronic energy surface of small clusters calculated within the generalized gradient approximation of density functional theory. This parametrization includes s and p angular momentum symmetries and parameters for the on-site, hopping and overlap matrix elements. With the aid of these new parameters, the global minima of silicon carbide clusters in the range of 10-30 atoms were discovered with the adaptive Monte Carlo Method [1]. The ATMC optimization process is fast and drives the system across configuration space very effectively reaching the global minimum in a small number of tempering events. Growth sequence, stability patterns, and temperature behavior were also obtained. [1] X. Dong and E. Blaisten-Barojas, J. of Comp. & Theor. Nanoscience, 3, 118-127 (2006). Estela Blaisten-Barojas Computational Materials Science Center, George Mason University, Fairfax, VA 22030 Date submitted: 02 Dec 2006 Electronic form version 1.4

Small carbon clusters metallized with Li were studied within a hybrid density functional approach with generalized gradient correction. Structures of the ground state and several excited states associated with different isomers and multiplicities were systematically calculated for CxLiy with x=1–3 and y=1–5. The most stable isomers are either linear or planar in the ground state. Three-dimensional structures are only identified for CLi4, CLi5, and C3Li4. There is important charge transfer in these compounds, showing that ionic bonding is favored as the cluster grows in size. Ionization potentials, electron affinities, and the vibrational analysis of all studied states is provided for all clusters. Structural transitions are predicted for C2Li2 at 1400K and C2Li4 at 420K.