Abstract
An ab initio study of quantum confinement of deuterium clusters in carbon nanotubes is presented. First, density functional theory (DFT)-based symmetry-adapted perturbation theory is used to derive parameters for a pairwise potential model describing the adsorbate-nanotube interaction. Next, we analyze the quantum nuclear motion of N D2 molecules (N < 4) confined in carbon nanotubes using a highly accurate adsorbate-wave-function-based approach, and compare it with the motion of molecular hydrogen. We further apply an embedding approach and study zero-point energy effects on larger hexagonal and heptagonal structures of 7-8 D2 molecules. Our results show a preference for crystalline hexagonal close packing hcp of D2 molecules inside carbon nanotubes even at the cost of a reduced volumetric density within the cylindrical confinement.
Highlights
Clean sources of energy and efficient energy storage are at the core of the current research in nanoscience and nanotechnology
We propose an additive pairwise potential model for the D(z12) for the (D2)–nanotube interaction which relies on high-level ab initio calculations using the SAPT(DFT) approach.[19,20]
We reduce our analysis to radial motions of the D2 molecules in a plane perpendicular to the tube axis
Summary
Clean sources of energy and efficient energy storage are at the core of the current research in nanoscience and nanotechnology. Very recent studies have addressed the possible existence of either a superfluid[12] or a crystalline phase[13,14] for parahydrogen molecules inside carbon nanotubes at zero temperature[12,14] or temperatures below 4 K,13 revealing the impact of quantum nuclear effects Motivated by active experimental research, the last few years have seen marked progress in the development of methods to describe the quantum nuclear motion of H2 and D2 isotopes encapsulated by carbon nanotubes, including diffusion dynamics These theoretical studies have provided explanations of relevant confinement effects such as the quantum-induced reversed trend in H2 and D2 diffusion rates upon lowering the temperature,[17] confirming the experimental
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