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Classical Density Functionals for Modelling Hydrogen Physisorption at 77 K

Martin B. Sweatman, Chemical and Process Engineering, University of Strathclyde, 75, Montrose Street, Glasgow, G11XJ, United Kingdom

This work [1] surveys techniques based on classical density functionals for modelling the quantum dispersion of physisorbed molecular hydrogen at 77 K. Two such techniques are examined in detail. The first is based on the ‘open ring approximation' (ORA) of Broukhno et.al. [2], and it is compared with a technique based on the semi-classical approximation of Feynman and Hibbs (FH). For both techniques, a classical density functional is used to model hydrogen molecule – hydrogen molecule (i.e. excess) interactions. Density functional results for a model of hydrogen adsorption into a graphitic slit pore at 77 K are compared with path-integral Monte-Carlo simulations. It is found that the ORA technique is flawed and that the best option is to combine the FH technique for hydrogen-surface interactions with an excess functional based on a calibrated hydrogen-hydrogen interaction.

[1] M.B. Sweatman, Physical Review E 77, 026712 (2008).

[2] A. Broukhno, P.N. Vorontsov-Velyaminov, and H. Bohr, Physical Review E 72, 046703 (2005).