The physical and chemical properties of tubular nanostructures of boron, boron nitride, gold, and zinc oxide have been theoretically studied. First, calculations using high-level ab initio methods suggest that double-ring tubular isomer of B 20 is likely the global minimum of neutral B 20 cluster. The planar-to-tubular structural transition starts at n =20 for neutral Bn clusters but should occur beyond n =20 for anion B n - clusters. Second, adsorption of chemical species H, O, CO, H 2 , O 2 , H 2 O and NH 3 at a perfect site (PS) and near a Stone-Wales (SW) defect on the sidewall of zigzag (8,0) and armchair (5,5) boron nitride (BN) single-walled nanotubes (SWNTs) was studied using density-functional theory (DFT) method. Reactivity near SW defect is generally higher than that at the PS due to the formation of frustrated B-B and N-N bonds and the local strain caused by pentagonal and heptagonal pairs. Third, a systematic DFT study on field-emission performance of prototype BN nanocones has shown that two 120°-BN nanocones are the promising candidates for the field-emission electron source based on their ionization potential and electron affinity. The doping/adsorption of an impurity atom is unfavorable to the field emission. Fourth, a DFT study of CO oxidation on Au helical (5,3) nanotubes suggests that CO oxidation is initiated by CO+O 2 [arrow right]OOCO[arrow right]CO 2 +O reaction, where a low activation barrier of 0.29eV and peroxo-type O-O-CO intermediate along the reaction pathway exist, and followed by CO +O[arrow right]CO 2 reaction with a barrier of 0.03eV. Fifth, a DFT study on the potential application of a prototype ZnO (6,0) zigzag SWNT as gas sensor for H 2 , O 2 , CO, NH 3 and NO 2 shows that the electron-donor molecules (CO and NH 3 ) tend to enhance the concentration of major carriers (electrons), whereas the electron-acceptor molecules (O 2 and NO 2 ) tend to reduce the concentration. O 2 and NO 2 can dissociate at the oxygen vacancy (VO) sites through filling the VO with one atomic O originated from the adsorbates. The dissociation of O 2 is exothermic and barrierless while the dissociation of NO 2 is also exothermic but entails a small activation barrier (0.49eV).
