Exploring CO₂@sI Clathrate Hydrates as CO₂ Storage Agents by Computational Density Functional Approaches

Abstract

The formation of specific clathrate hydrates and their transformation at given thermodynamic conditions depends on the interactions between the guest molecule/s and the host water lattice. Understanding their structural stability is essential to control structure‐property relations involved in different technological applications. Thus, the energetic aspects relative to CO2@sI clathrate hydrate are investigated through the computation of the underlying interactions, dominated by hydrogen bonds and van der Waals forces, from first‐principles electronic structure approaches. The stability of the CO2@sI clathrate is evaluated by combining bottom‐up and top‐down approaches. Guest‐free and CO2 guest‐filled aperiodic cages, up to the gradually CO2 occupation of the entire sI periodic unit cells were considered. Saturation, cohesive and binding energies for the systems are determined by employing a variety of density functionals and their performance is assessed. The dispersion corrections on the non‐covalent interactions are found to be important in the stabilization of the CO2@sI energies, with the encapsulation of the CO2 into guest‐free/empty cage/lattice being always an energetically favorable process for most of the functionals studied. The PW86PBE functional with XDM or D3(BJ) dispersion corrections predicts a lattice constant in accord to the experimental values available, and simultaneously provides a reliable description for the guest‐host interactions in the periodic CO2@sI crystal, as well as the energetics of its progressive single cage occupancy process. It has been found that the preferential orientation of the single CO2 in the large sI crystal cages has a stabilizing effect on the hydrate, concluding that the CO2@sI structure is favored either by considering the individual building block cages or the complete sI unit cell crystal. Such benchmark and methodology cross‐check studies benefit new data‐driven model research by providing high‐quality training information, with new insights that indicate the underlying factors governing their structure‐driven stability, and triggering further investigations for controlling the stabilization of these promising long‐term CO2 storage materials.

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.…”

“…Regarding the description of the underlying guest-host molecular interactions, several computational approaches are nowadays available, ranging from the most accurate wavefunction(WF)-based methods to the computationally more viable density-functional theory (DFT) ones. 38,[54][55][56][57][58][59][60][61] Following our previous efforts in the field, in this study we report well-converged reference data from wavefunction-based electronic structure methods, that serve to systematically evaluate the performance of conventional and modern density functional approaches. In general, the dispersioncorrected density functional methods prevail the conventional functionals, 62 however for certain type of vdW systems, like gas clathrate hydrates, may not be the case and their assessment is still necessary.…”

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

“…The counterpoise (CP) corrections, 85 ECP, were applied to energies to reduce the basis set superposition error (BSSE) effects in the present calculations. On the basis of previous studies, [60][61][62][63][67][68][69] we choose to employ the revPBE, PW86PBE, and B3LYP functionals in the DFT calculations using the standard implementation in the LIBXC library. 86 The additional dispersion corrections are included using the exchange dipole moment (XDM), D3, and D4 many-body schemes, [87][88][89][90][91] as implemented in the POSTG code 92 and DFTD3/DFTD4 programs, 93,94 respectively.…”

“…Although both XDM and D4 dispersion schemes exhibit similar behavior on the energetics of the CO 2 @sII clathrates, which are predicted to be more stable than the CO 2 @sI ones, compared to their release energy of −46.09 kcal/mol reported in previous PW86PBE-XDM calculations. 60,69 Thus, in Fig. 7 (see the right panel) and Table S4 (see the supplementary material), we present the results obtained on structural properties of the CO…”

“…[71][72][73][74][75] Thus, in the framework of the CO 2 clathrates, we performed DFT-D calculations on the structural properties and stability of the sII structure by considering the guest-host (cage/s) interactions in finite-size clathrate-like cages, where valuable additional information can also be obtained from ab initio wavefunction (WF) based calculations, as well as guest-host (lattice) effects in the complete sII unit cell. On the basis of previous investigations on CO 2 @sI clathrates, 60,62,63,[67][68][69] specific exchangecorrelation functionals were employed in the CO 2 @sII case, including dispersion corrections, in order to fully represent the underlying interactions.…”