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In this work, we examine the kink-nucleation process in BCC screw dislocations using atomistic simulation and transition pathway analysis, with a particular focus on the compact core structure. We observe the existence of a threshold stress, which results in an abrupt change in the minimum energy path of the kink-nucleation process, and hence, a discontinuity in the activation energy versus stress for the process. The magnitude of the discontinuity is found to be related to the degree of metastability of an intermediate split-core structure. This feature appears to be a direct consequence of the so-called 'camel-hump' nature of the Peierls potential, which manifests itself in the existence of a metastable, intermediate split-core structure. The effect is observed in a number of empirical EAM potentials, including Fe, Ta, V, Nb and Mo, suggesting a generality to the observations.

In this paper, density functional theory is used to estimate hydrogen adsorption in a novel carbonaceous material, single-walled carbon nanotubes. An idealized adsorbent structure for the nanotubes is assumed. We have mapped out the regime of operating pressures and temperatures where an adsorption-based storage system is expected to deliver more hydrogen than a similar system of compressed gas. This regime is also a function of pore size. We have calculated the overall hydrogen volumetric and gravimetric density within the framework of a typical high-pressure gas storage system. Within the regime of operating conditions where adsorptive storage seems attractive, the storage properties of hydrogen in a carbon nanotube system appear to fall far short of the targets of 62 kg of H2/m3 and 6.5 wt % H2 set by the Department of Energy. The computed gravimetric storage densities also fall short of those reported in the literature (Nature 1997, 386, 377). We discuss several possible mechanisms by which higher gravimetric density could be rationalized, including chemisorption, adsorption at interstitial sites, and swelling of the nanotube array.

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The properties of alkanes in the C20–C40 mass range are of fundamental importance in industrial applications as they are important constituents of synthetic lubricant base stocks. In an extension to earlier work on alkanes in the C20–C40 carbon number range we present the results of molecular simulations for 9-octylheptadecane, a starlike isomer of C25. Both equilibrium (EMD) and nonequilibrium molecular dynamics (NEMD) simulations have been performed under ambient state conditions and to pressures in the gigapascal range. The EMD simulations focus on calculations of the rotational relaxation times, while the NEMD simulations reveal the dependence of the viscosity on strain rate. Additionally, we calculate the viscosity number and pressure–viscosity coefficient for 9-octylheptadecane and compare the results with those obtained experimentally.