Computational density-functional approaches on finite-size and guest-lattice effects in CO2@sII clathrate hydrate

Abstract

We performed first-principles computations to investigate guest-host/host-host effects on the encapsulation of the CO 2 molecule in sII clathrate hydrates from finite-size clusters up to periodic 3D crystal lattice systems. Structural and energetic properties were first computed for the individual and first-neighbors clathrate-like sII cages, where highly accurate ab initio quantum chemical methods are available nowadays, allowing in this way the assessment of the density functional (DFT) theoretical approaches employed. The performance of exchange-correlation functionals together with recently developed dispersion-corrected schemes was evaluated in describing interactions in both short-range and long-range regions of the potential. On this basis, structural relaxations of the CO 2 -filled and empty sII unit cells yield lattice and compressibility parameters comparable to experimental and previous theoretical values available for sII hydrates. According to these data, the CO 2 enclathration in the sII clathrate cages is a stabilizing process, either by considering both guest-host and host-host interactions in the complete unit cell or only the guest-water energies for the individual clathrate-like sII cages. CO 2 @sII clathrates are predicted to be stable whatever the dispersion correction applied and in the case of single cage occupancy are found to be more stable than the CO 2 @sI structures. Our results reveal that DFT approaches could provide a good reasonable description of the underlying interactions, enabling the investigation of formation and transformation processes as a function of temperature and pressure.

Assessment of DFT approaches in noble gas clathrate-like clusters: stability and thermodynamics

“…Looking for a computational affordable method to calculate energies in larger systems up to crystalline hydrate frameworks, we have also assessed the performance of different DFT functionals. Specifically, we have consider those functionals which showed a better behavior in previous studies of clathratelike systems, 35,43,45,58,61,72 namely the PW86PBE, 73,74 revPBE, 75 B3LYP 76 and PBE0 77 functionals, together with dispersion corrections, such as the original zero-damping function, D3(0), 78 as well as the most popular Becke-Johnson damping function, D3(BJ), 79 the most recent developed, D4, 80,81 and the exchange-hole dipole moment (XDM) model. 82 All the DFT calculations were performed using Gaussian 83 and Orca 65 (in the case of the revPBE and B3LYP functionals) packages with the additional dispersion corrections computed by the DFT-D3, 84 DFT-D4 85 and POSTG 86,87 programs.…”

Encapsulation of a Water Molecule inside C60 Fullerene: The Impact of Confinement on Quantum Features

“…In view of the complexity of the problem, most of the previous studies , have highlighted the importance of fully coupled quantum treatments of both nuclear and electronic degrees of freedom of such nine-dimensional (9D) guest–host systems. Thus, our current investigation ,− aims to contribute to the field by proposing a systematic protocol to crosscheck first-principles methodologies on noncovalent guest–host interactions and an efficient procedure within the multiconfiguration time-dependent Hartree (MCTDH) framework , to treat the nuclear quantum dynamics of any nanoconfined light molecule. Here, our efforts are focused on fully coupled quantum treatments employing available three-dimensional (3D) and six-dimensional (6D) potentials for the isolated and enclathrated H 2 O molecule, respectively.…”

Delving into guest-free and He-filled sI and sII clathrate hydrates: a first-principles computational study

“…The bulk modulus obtained for the He@sI/sII clathrates at PW86PBE-XDM/D4 level (Table 1) are smaller than those obtained for other systems. 3,12 For example, for the CO 2 @sI hydrate values of 13.64/12.53 GPa for the bulk modulus have been recently reported, while in the He@sI the values obtained are 12.140/10.632 GPa for the same functionals. In the case of CO 2 @sII, these values are 17.149/16.053 GPa, whereas for the He@sII hydrate we obtained 15.851/15.084 GPa.…”

“…Therefore, transitions between different phases can occur or even several structures can coexist. 3 Is it important to emphasize the need to understand the stability of these systems, taking into account nuclear quantum effects, 26,27 as well as the mechanisms involved in their formation/dissociation, 28 since new structures can be found by both filling with guest molecules 23 or by emptying 16,29 the corresponding hydrate cavities or even the inter-cage molecule migration of one cage to the neighboring ones, [30][31][32] under certain P-T conditions. 33 This may be useful and relevant, not only from a fundamental point of view, given that new regimes of the phase diagram of water can be investigated, such as low-density ice structures, 34,35 but also from a practical point of view, since promising applications of gas hydrates can be further explored, such as gas storage materials, [36][37][38] potential energy sources, 39,40 gas separation, [41][42][43] energy transport 44,45 and desalination techniques.…”

“…Clathrate hydrates are crystalline compounds formed by a host water skeleton containing polyhedral cavities of different size and shape, which can be occupied, fully or partially, by diverse guest molecules (noble gases, H 2 , N 2 , CH 4 , CO 2 , H 2 S,…) depending mostly on the thermodynamic conditions (low temperature and high pressure). 1–3 These ice-like lattices are naturally occurring in the ocean depths, as well as in permafrost regions of Earth. 4,5 Moreover, they are also likely to exist in other planetary bodies, such as Pluto's ocean, 6 Mars’ ice caps 7 or Titan's surface.…”