We propose structural and electronic properties of recently synthesized SiC nanotubes. The nanotubes with a Si to C ratio of 1:1 exhibit rich morphologies and are shown to belong to two distinct categories that are close in energies but show significant differences in electronic and transport properties. Similarities and differences are invoked with the case of BN nanotubes to explain the observed surface reconstruction.

A minimal parameter tight-binding molecular-dynamics scheme incorporating a Hubbard Hamiltonian for the treatment of magnetic effects is detailed. The computational efficiency of the scheme allows applications to cluster sizes well beyond the range of ab initio techniques. The method is used to obtain magnetic moments of Ni, Fe, and Co clusters in excellent agreement with experiment. ͓S0163-1829͑98͒01416-7͔

Quantum conductivity of single-wall carbon nanotube Y-junctions is calculated. The current versus voltage characteristics of these junctions show asymmetry and rectification, in agreement with recent experimental results. Furthermore, rectification is found to be independent of the angle between the branches of these junctions, indicating this to be an intrinsic property of symmetric Y-junctions. The implications for the Y-junction to function as a nanoscale molecular electronic switch are investigated.

The design and performance optimization of future nanocatalysts will depend on our understanding of adsorbate-metal interactions. Using first principle calculations, we identify suitable descriptors, namely, the coordination number and curvature angle of the surface Au atoms, capable of predicting the CO binding strength on every site of Au nanoparticles. Our results unravel how the size, shape, and symmetry of nanoparticles affect their electronic properties and, consequently, their interaction with CO. Importantly, these descriptors can be successfully applied to other metals using structural inputs from experiments and/or molecular modeling.

The optical properties of ZnO nanowires containing defects are investigated using first-principles densityfunctional theory incorporating the LDA+ U formalism. Calculations include defects in the form of substitutional N, Zn, and O vacancies as well as +1 charged O vacancy. Our calculations reveal that the presence of vacancies contribute strongly to optical absorption in the visible. Furthermore, the presence of +1 charged O vacancy is found to result in a blueshift of the absorption peaks, reducing the number of wavelengths that can be absorbed in the visible. These findings can be a useful tool for the design of new generation of materials with improved solar radiation absorption.