Path integral Monte Carlo simulations of H2 adsorbed to lithium-doped benzene: A model for hydrogen storage materials

Abstract

Finite temperature quantum and anharmonic effects are studied in H 2 -Li + -benzene, a model hydrogen storage material, using path integral Monte Carlo (PIMC) simulations on an interpolated potential energy surface (PES) refined over the eight intermolecular degrees of freedom based upon M05-2X/6-311+G(2df,p) density functional theory calculations. Rigidbody PIMC simulations are performed at temperatures ranging from 77 K to 150 K, producing both quantum and classical probability density histograms describing the adsorbed H 2 . Quantum effects broaden the histograms with respect to their classical analogues and increase the expectation values of the radial and angular polar coordinates describing the location of the center-of-mass of the H 2 molecule. The rigid-body PIMC simulations also provide estimates of the change in internal energy, ∆U ads , and enthalpy, ∆H ads , for H 2 adsorption onto Li + -benzene, as a function of temperature. These estimates indicate that quantum effects are important even at room temperature and classical results should be interpreted with caution. Our results also show that anharmonicity is more important in the calculation of U and H than coupling-coupling between the intermolecular degrees of freedom becomes less important as temperature increases whereas anharmonicity becomes more important. The most anharmonic motions in H 2 -Li + -benzene are the "helicopter" and "ferris wheel" H 2 rotations. Treating these motions as one-dimensional free and hindered rotors, respectively, provides simple corrections to standard harmonic oscillator, rigid rotor thermochemical expressions for internal energy and enthalpy that encapsulate the majority of the anharmonicity. At 150 K, our best rigid-body PIMC estimates for ∆U ads and ∆H ads are −13.3 ± 0.1 and −14.5 ± 0.1 kJ.mol −1 , respectively. a) Electronic

Mechanism of Hydrogen Storage in the Graphene Nanoflake–Lithium–H2 System

“…The binding energy was calculated to be 4.7 kcal/mol at the CCSD­(T)/MP2 level. More recently, D’Arcy et al investigated the Bz–Li–(H 2 ) n system ( n = 1, 2) using quantum Monte Carlo simulations , and obtained binding energies of 4.5 ( n = 1) and 3.2 kcal/mol ( n = 2). Zhu et al calculated the binding energy using a larger aromatic hydrocarbon GR(14) composed of 14 benzene rings.…”

Snowball formation for Cs+ solvation in molecular hydrogen and deuterium

“…), hence, it is worth exploring the impact of this alternative quantum solvent. There is also much interest in H 2 -M + interactions for applications of reversible storage of hydrogen in porous materials, [7][8][9][10][11] where dopant metal cations act as centers to which hydrogen molecules attach. Moreover, different nuclear quantum effects in H 2 and D 2 have been proposed to exploit selective adsorption 12 and isotope separation 13 in metal-doped materials, processes of paramount importance for the development of new fusion reactors.…”

“…Our goal is to investigate whether well-defined and compact shells are formed and what their structure is. In addition, since the H 2 -Cs + interaction is very anisotropic, we believe that it is worth studying the H 2 /D 2 orientational effects 10,31,32 by explicitly taking into account their rotational degrees of freedom and comparing with the more widely used pseudoatom model. The importance of three-body (3B) induction forces [33][34][35][36] is assessed as well.…”

Complexes of Alkali Metal Cations and Molecular Hydrogen: Potential Energy Surfaces and Bound States

“…1,2 In addition, in the study of the interstellar medium there is interest in processes involving ubiquitous H 2 molecules and relatively abundant metallic cations. [3][4][5] Another motivation for studying these systems is their application in processes of reversible storage of hydrogen in porous materials, [6][7][8][9][10] where dopant metal cations act as centers to which hydrogen molecules attach and isotopic substitution effects (D 2 by H 2 ) have been found to be relevant. 11 In all these cases, it is also interesting to study the differences in the interaction depending on whether the molecule is in the ground rotational state (para-H 2 , ortho-D 2 ) or in the first rotationally excited state (ortho-H 2 , para-D 2 ), as has been found in related works.…”