An Accurate and Transferable Intermolecular Diatomic Hydrogen Potential for Condensed Phase Simulation

Belof, Jonathan L.; Stern, Abraham C.; Space, Brian

doi:10.1021/ct800155q

Cited by 91 publications

(182 citation statements)

References 44 publications

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“…Note, the experimental isotherms that are shown in Figure 3(a) were estimated from reference 11. The H 2 potential used in this work is a five-site polarizable model that was developed from first principles previously by Belof et al 78 It can be seen that simulations using this model generated an isotherm that is in very good agreement with experiment at 77 K. The calculated hydrogen sorption isotherm and the experimental isotherm at 77 K are nearly equivalent to within joint uncertainties (the maximum calculated error is ±0.04 wt %). The greatest deviation between experiment and simulation at 77 K can be observed at pressures lower than 0.20 atm, where simulation slightly oversorbs experiment.…”

Section: B Many-body Polarizationmentioning

confidence: 59%

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Pham

Forrest

Hogan

et al. 2015

Crystal Growth & Design

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Grand canonical Monte Carlo (GCMC) simulations of hydrogen sorption were performed in In-soc-MOF, a charged metal-organic framework (MOF) that contains In3O trimers coordinated to 5,5 -azobis-1,3-benzenedicarboxylate linkers. The MOF contains nitrate counterions that are located in carcerand-like capsules of the framework. This MOF was shown to have a high hydrogen uptake at 77 K and 1.0 atm. The simulations were performed with a potential that includes explicit many-body polarization interactions, which were important for modeling gas sorption in a charged/polar MOF such as In-soc-MOF. The simulated hydrogen sorption isotherms were in good agreement with experiment in this challenging platform for modeling. The simulations predict a high initial isosteric heat of adsorption, Qst, value of about 8.5 kJ mol −1 , which is in contrast to the experimental value of 6.5 kJ mol −1 for all loadings. The difference in the Qst behavior between experiment and simulation is attributed to the fact that, in experimental measurements, the sorbate molecules cannot access the isolated cages containing the nitrate ions, the most energetically favorable site in the MOF, at low pressures due to an observed diffusional barrier. In contrast, the simulations were able to capture the sorption of hydrogen onto the nitrate ions at low loading due to the equilibrium nature of GCMC simulations. The experimental Qst values were reproduced in simulation by blocking access to all of the nitrate ions in the MOF. Furthermore, at 77 K, the sorbed hydrogen molecules were reminiscent of a dense fluid in In-soc-MOF starting at approximately 5.0 atm, and this was verified by monitoring the isothermal compressibility, βT , values. The favorable sites for hydrogen sorption were identified from the polarization distribution as the nitrate ions, the In3O trimers, and the azobenzene nitrogen atoms. Lastly, the two-dimensional quantum rotational levels for a hydrogen molecule sorbed about the aforementioned sites were calculated and the transitions were in good agreement to those that were observed in the experimental inelastic neutron scattering (INS) spectra.

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Section: B Many-body Polarizationmentioning

confidence: 59%

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Pham

Forrest

Hogan

et al. 2015

Crystal Growth & Design

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“…These were calculated using the Lennard-Jones 12-6 potential, partial charges with Ewald summation, 41 50 and the fivesite polarizable model also developed by Belof et al 50 These models are denoted Buch, DL, BSS, and BSSP, respectively. The simulated results are presented for the polarizable potential; however, the simulated H 2 sorption isotherms and Q st values for the other models in both ZIFs are discussed where appropriate, with data shown in the Supporting Information ( Figures S6 and S12).…”

Section: B Theoretical Sectionmentioning

confidence: 99%

High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

et al. 2017

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A combined experimental and theoretical study of H2 sorption was carried out on two isostructural zeolitic imidazolate frameworks (ZIFs), namely ZIF-68 and ZIF-69. The former consists of Zn 2+ ions that are coordinated to two 2-nitroimidazolate and two benzimidazolate linkers in a tetrahedral fashion, while 5-chlorobenzimidazolate is used in place of benzimidazolate in the latter compound. H2 sorption measurements showed that the two ZIFs display similar isotherms and isosteric heats of adsorption (Qst). The experimental initial H2 Qst value for both ZIFs was determined to be 8.1 kJ mol −1 , which is quite high for materials that do not contain exposed metal centers. Molecular simulations of H2 sorption in ZIF-68 and ZIF-69 confirmed the similar H2 sorption properties between the two ZIFs, but also suggest that H2 sorption is slightly favored in ZIF-68. This work also presents inelastic neutron scattering (INS) spectra for H2 sorbed in ZIFs for the first time. The spectra for ZIF-68 and ZIF-69 shows a broad range of intensities starting from about 4 meV. The most favorable H2 sorption site in both ZIFs correspond to a confined region between two adjacent 2-nitroimidazolate linkers. Two-dimensional quantum rotation calculations for H2 sorbed at this site in ZIF-68 and ZIF-69 produced rotational transitions that are in accord with the lowest energy peak observed in the INS spectrum for the respective ZIFs. We found that the primary binding site for H2 in the two ZIFs generates high barriers to rotation for the adsorbed H2, which are greater than those in several metal-organic frameworks (MOFs) which possess openmetal sites. H2 sorption was also observed for both ZIFs in the vicinity of the nitro groups of the 2-nitroimidazolate linkers. This study highlights the constructive interplay of experiment and theory to elucidate critical details of the H2 sorption mechanism in these two isostructural ZIFs.

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“…32 Additionally, it will be shown that the rotational barrier for H 2 at the most favorable sorption site in [Zn(trz)(tftph)] is among the highest of reported MOF materials based on INS measurements and calculations. 45 For simulations using the BSSP model, polarization was included explicitly in the simulations via a Thole-Applequist type model. [46][47][48] All simulations were performed in the rigid 2 × 2 × 2 system cell of the MOF as shown in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Investigating H₂ Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering

et al. 2015

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Simulations of H2 sorption were performed in a metal-organic framework (MOF) consisting of Zn(2+) ions coordinated to 1,2,4-triazole and tetrafluoroterephthalate ligands (denoted [Zn(trz)(tftph)] in this work). The simulated H2 sorption isotherms reported in this work are consistent with the experimental data for the state points considered. The experimental H2 isosteric heat of adsorption (Qst) values for this MOF are approximately 8.0 kJ mol(-1) for the considered loading range, which is in the proximity of those determined from simulation. The experimental inelastic neutron scattering (INS) spectra for H2 in [Zn(trz)(tftph)] reveal at least two peaks that occur at low energies, which corresponds to high barriers to rotation for the respective sites. The most favorable sorption site in the MOF was identified from the simulations as sorption in the vicinity of a metal-coordinated H2O molecule, an exposed fluorine atom, and a carboxylate oxygen atom in a confined region in the framework. Secondary sorption was observed between the fluorine atoms of adjacent tetrafluoroterephthalate ligands. The H2 molecule at the primary sorption site in [Zn(trz)(tftph)] exhibits a rotational barrier that exceeds that for most neutral MOFs with open-metal sites according to an empirical phenomenological model, and this was further validated by calculating the rotational potential energy surface for H2 at this site.

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An Accurate and Transferable Intermolecular Diatomic Hydrogen Potential for Condensed Phase Simulation

Cited by 91 publications

References 44 publications

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

Investigating H₂ Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering

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An Accurate and Transferable Intermolecular Diatomic Hydrogen Potential for Condensed Phase Simulation

Cited by 91 publications

References 44 publications

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

High H2 Sorption Energetics in Zeolitic Imidazolate Frameworks

Investigating H2 Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering

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Product

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High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

Investigating H₂ Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering