Ab initio modelling of molecular hydrogen rotation in the outside of carbon nanotubes

ABSTRACT

A first-principle modelling of hydrogen molecular rotation in the outside of carbon nanotubes is presented. Density functional theory (DFT)-based symmetry-adapted perturbation theory (SAPT) is first applied to analyse the influence of the rotation on the dispersion and dispersionless H${}_2$-nanotube interaction for both sub- and nanometer-sized tubes. An adsorbate three-dimensional wave-function treatment is then applied to calculate the molecular energy levels of the rotating hydrogen molecule. As a key difference with the H${}_2$ located inside the tubes, the SAPT-based analysis indicates a marked influence of a nanotube curvature-induced dipole on the angular-dependent balance of exchange-repulsion, electrostatic, and dispersion contributions for narrow nanotubes. As a result, the landscape of molecular energy levels depends strongly on the diameter of the porous material. In addition, an effective one-dimensional model is proposed to account for the nuclear motion, reproducing full-dimensional approach within less than 1%.

GRAPHICAL ABSTRACT

Keywords:

• Carbon nanotubes
• quantum confinement
• molecular hydrogen rotation
• curvature-dependent dipole

Acknowledgements

M.P.d.L.C. is greatly thankful to the CTI (CSIC) and CESGA super-computer facilities (Spain) for the provided computational resources.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work has been partly supported by the Spanish Agencia Estatal de Investigación (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER, UE) under grant no. MAT2016-75354-P and COST Action CM1405 ‘Molecules in Motion’ (MOLIM).