Molecular-Dynamics and First-Principles Calculations of Raman Spectra and Molecular and Electronic Structure of Hydrogen Clusters in Hydrogen Clathrate Hydrate

Wang, Jianwei; Lu, Hailong; Ripmeester, John A.; Becker, Udo

doi:10.1021/jp106788u

Cited by 31 publications

(29 citation statements)

References 51 publications

(164 reference statements)

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“…Determination of thermodynamic properties requires an extensive sampling of the system configuration space that strongly related to the topology of the underlying potential energy surface the electronic calculations can be considered as an accurate approach for the potential model, although for systems of quite limited size. 27 Thus, model potentials based on less computationally demanding force fields have been employed usually for the description of water interaction. [28][29][30][31][32] Here, we choose the TIP4P/ice water model 33 as it has been found to give the best description of the phase diagram of the water and its polymorphs in the solid state, as well as the coexistence lines in clathrate hydrate systems.…”

Section: Introductionmentioning

confidence: 99%

High Pressure Structural Transitions in Kr Clathrate-Like Clusters

2016

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Classical thermodynamic properties of a size-specific Kr clathrate-like cluster, modeled by an ab initio and a semiempirical Kr-water potential, were computed from parallel-tempering Monte Carlo simulations. The temperature and pressure dependence of the cluster's heat capacity was studied, and phase diagrams were constructed using a multiple-histogram method. By associating the heat capacity (maxima) and the Pearson correlation coefficient (minima/maxima) values with the phase transitions, attempts were made to identify such changes to particular cluster structures. Various isomers were computed by local optimizations of the interaction enthalpy at a set of randomly selected configurations at each temperature-pressure grid point. Their energy distributions and relative abundances were then employed to assign the observed phase transitions of the cluster. It was found that the structural changes at high pressures are related to Kr clathrate-like cages, such as those of the sI, sII and sH hydrates, as well as a new one at higher pressures, formed by tetragons and pentagons. Such transitions, at low temperatures and as pressure increases, are related to the topology of the intermolecular interactions, that are getting accessible by the sampling in the MC simulations, through the employed volume model.

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Section: Introductionmentioning

confidence: 99%

High Pressure Structural Transitions in Kr Clathrate-Like Clusters

2016

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“…[11][12][13] The potential cage occupancies have been investigated by experiment and theory in the past, with the major uncertainty being the occupancy of the 5 12 cages. 2,4,[14][15][16] Vibrational frequency shifts are one of the major sources of information about the cage occupancies due to their dependence on the local environment. In order to use the information contained in experimentally observed H 2 frequency shifts, a relationship between these frequency shifts and structural and dynamical properties of hydrogen clathrates needs to be established.…”

Section: Introductionmentioning

confidence: 99%

“…In order to address this problem, DFT has been combined with empirical force fields for the calculation of the frequency shifts. 16 Based on the coordinates from molecular dynamics (MD) simulations, structures of hydrogen containing clathrate cages were optimized using DFT calculations and harmonic frequencies were calculated based on these optimized structures. 16 However, frequency calculations on optimized structures do not include temperature effects.…”

Section: Introductionmentioning

confidence: 99%

“…16 Based on the coordinates from molecular dynamics (MD) simulations, structures of hydrogen containing clathrate cages were optimized using DFT calculations and harmonic frequencies were calculated based on these optimized structures. 16 However, frequency calculations on optimized structures do not include temperature effects. Furthermore, no quantum dynamical effects were taken into account in these calculations.…”

Section: Introductionmentioning

confidence: 99%

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The effect of classical and quantum dynamics on vibrational frequency shifts of H2 in clathrate hydrates

Plattner

Meuwly

2014

The Journal of Chemical Physics

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Vibrational frequency shifts of H2 in clathrate hydrates are important to understand the properties and elucidate details of the clathrate structure. Experimental spectra of H2 in clathrate hydrates have been measured for different clathrate compositions, temperatures, and pressures. In order to establish reliable relationships between the clathrate structure, dynamics, and observed frequencies, calculations of vibrational frequency shifts in different clathrate environments are required. In this study, a combination of classical molecular dynamics simulations, electronic structure calculations, and quantum dynamical simulation is used to calculate relative vibrational frequencies of H2 in clathrate hydrates. This approach allows us to assess dynamical effects and simulate the change of vibrational frequencies with temperature and pressure. The frequency distributions of the H2 vibrations in the different clathrate cage types agree favorably with experiment. Also, the simulations demonstrate that H2 in the 5(12) cage is more sensitive to the details of the environment and to quantum dynamical effects, in particular when the cage is doubly occupied. We show that for the 5(12) cage quantum effects lead to frequency increases and double occupation is unlikely. This is different for the 5(12)6(4) cages for which higher occupation numbers than one H2 per cage are likely.

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“…20), there are also reports that propose double occupancy or that find inconclusive evidence. [21][22][23][24][25] On the other hand, the larger T cage can store four H 2 molecules. If a fifth molecule is added, it escapes through one of the hexagonal faces into the neighboring, empty T cage.…”

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confidence: 99%

Ab initioenergetics and kinetics study of H2and CH4in the SI clathrate hydrate

Kolb

Román-Pérez

et al. 2011

Phys. Rev. B

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We present ab initio results at the density functional theory level for the energetics and kinetics of H 2 and CH 4 in the SI clathrate hydrate. Our results complement a recent article by some of the authors [G. Román-Pérez et al., Phys. Rev. Lett. 105, 145901 (2010)] in that we show additional results of the energy landscape of H 2 and CH 4 in the various cages of the host material, as well as further results for energy barriers for all possible diffusion paths of H 2 and CH 4 through the water framework. We also report structural data of the low-pressure phase SI and the higher-pressure phases SII and SH. Clathrate hydrates are crystalline, ice-like structures formed out of water molecules.1 The water framework creates cavities in which gas molecules-typically O 2 , H 2 , CO 2 , CH 4 , Ar, Kr, Xe-can be trapped, which stabilize the framework. The existence of clathrates was first documented in 1810 by Sir Humphry Davy, and clathrates became the subject of intensive studies in the 1930s, when oil companies became aware that clathrates can block pipelines.2 Nowadays, clathrate hydrates are of particular interest for two reasons: (i) they are formed naturally at the bottom of the ocean, where they are often filled with CH 4 .3 These deposits mean a tremendous stock pile of energy, while-at the same time-representing a possible global warming catastrophe if released uncontrolled into the environment through melting; (ii) clathrate hydrates can be used to store H 2 in its cavities and can be a viable hydrogen-storage material (albeit with moderate hydrogen-storage density). 4 For both cases, an understanding of the interaction between the guest molecule and the host framework is crucial for their formation and melting processes, which are still poorly understood. 5 In this brief report, we present results that elucidate this crucial guest-molecule/hostframework interaction and complement a recent paper by some of the authors. 6 We show additional results of the energy landscape of H 2 and CH 4 in the various cages of the host material, and we show further results for energy barriers for all possible diffusion paths of H 2 and CH 4 through the water framework. We also report structural data of the phases SI, SII, and SH.At low pressure, the methane-filled clathrate forms the structure SI, consisting of two types of cages. Guest molecules such as H 2 and CH 4 in the cavities of the clathrate hydrates interact with the water framework through van der Waals forces. But even the water framework itself, i.e., the interaction of water molecules through hydrogen bonds, has a van der Waals component. 9 To capture these effects, we perform here density functional theory (DFT) calculations utilizing the truly nonlocal vdW-DF functional, which includes van der Waals interactions seamlessly into DFT. [10][11][12] We implemented vdW-DF using a very efficient FFT formulation 13 into the latest release of PWSCF, which is a part of the QUANTUM-ESPRESSO package.14 For our calculations we used ultrasoft pseudopotentials with a kinet...

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Molecular-Dynamics and First-Principles Calculations of Raman Spectra and Molecular and Electronic Structure of Hydrogen Clusters in Hydrogen Clathrate Hydrate

Cited by 31 publications

References 51 publications

High Pressure Structural Transitions in Kr Clathrate-Like Clusters

High Pressure Structural Transitions in Kr Clathrate-Like Clusters

The effect of classical and quantum dynamics on vibrational frequency shifts of H2 in clathrate hydrates

Ab initioenergetics and kinetics study of H2and CH4in the SI clathrate hydrate

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