We studied various gas molecules (NO 2 , O 2 , NH 3 , N 2 , CO 2 , CH 4 , H 2 O, H 2 , Ar) on single-walled carbon nanotubes (SWNTs) and bundles using first principles methods. The equilibrium position, adsorption energy, charge transfer, and electronic band structures are obtained for different kinds of SWNTs.Most molecules adsorb weakly on SWNTs and can be either charge donor or acceptor to the nanotubes. We find the gas adsorption on the bundle interstitial and groove sties is stronger than that on an individual tube. The electronic properties of SWNTs are sensitive to the adsorption of certain gases such as NO 2 and O 2 . Charge transfer and gas-induced charge fluctuation might significantly affect the transport properties of SWNTs. Our theoretical results are consistent with recent experiments. 73.61.Wp, 73.20.Hb, 34.50.Dy, 82.65.My Typeset using REVT E X 1 16

We studied Li-intercalated carbon nanotube ropes by first-principles methods. Results show charge transfer between Li and C and small structural deformation due to intercalation. Both the interior of the nanotube and the interstitial space are susceptible for intercalation. The Li intercalation potential of a single-walled nanotube rope is comparable to that of graphite and almost independent of the Li density up to around LiC2, as observed in recent experiments. This density is significantly higher than that of Li-intercalated graphite, making the nanorope a promising candidate for the anode material in battery applications.

Quantum transport properties of intermolecular nanotube contacts are investigated. We find that atomic structure in the contact region plays important roles and resistance of contacts varies strongly with geometry and nanotube chirality. Nanotube end-end contacts have low resistance and show negative differential resistance (NDR) behavior. Contact resistance can be dramatically decreased by exerting small pressure/force between the tubes if the contact is commensurate. Significant variation and nonlinearity of contact resistance may lead to new device applications.Comment: 4 pages, 4 figure

The structures of free-standing gold nanowires are studied by using molecular-dynamics-based genetic algorithm simulations. Helical and multiwalled cylindrical structures are found for the thinner nanowires, while bulk-like fcc structures eventually form in the thicker nanowires up to 3 nm in diameter. This noncrystalline-crystalline transition starts from the core region of nanowires. The vibrational, electronic, and transport properties of nanowires are investigated based on the optimal structures. Bulklike behaviors are found for the vibrational and electronic properties of the nanowires with fcc crystalline structure. The conductance of nanowires generally increases with wire diameter and depends on the wire structure.

A carbon nanotube is an ideal object for understanding the atomic scale aspects of interface interaction and friction. Using molecular statics and dynamics methods different types of motion of nanotubes on a graphite surface are investigated. We found that each nanotube has unique equilibrium orientations with sharp potential energy minima. This leads to atomic scale locking of the nanotube. The effective contact area and the total interaction energy scale with the square root of the radius. Sliding and rolling of nanotubes have different characters. The potential energy barriers for sliding nanotubes are higher than that for perfect rolling. When the nanotube is pushed, we observe a combination of atomic scale spinning and sliding motion. The result is rolling with the friction force comparable to sliding.Comment: 4 pages (two column) 6 figures - one ep