Modeling of Structure H Carbon Dioxide Clathrate Hydrates: Guest–Lattice Energies, Crystal Structure, and Pressure Dependencies

Abstract

We performed first-principles computations to investigate the complex interplay of molecular interaction energies in determining the lattice structure and stability of CO 2 @sH clathrate hydrates. Density functional theory computations using periodic boundary conditions were employed to characterize energetics and the key structural properties of the sH clathrate crystal under pressure, such as equilibrium lattice volume and bulk modulus. 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. Structural relaxations of the fully CO 2 -filled and empty sH unit cells yield crystal structure and lattice energies, while their compressibility parameters were derived by including the pressure dependencies. The present quantum chemistry computations suggest anisotropy in the compressibility of the sH clathrate hydrates, with the crystal being less compressible along the a -axis direction than along the c -axis one, in distinction from nearly isotropic sI and sII structures. The detailed results presented here give insight into the complex nature of the underlying guest–host interactions, checking earlier assumptions, providing critical tests, and improving estimates. Such entries may eventually lead to better predictions of thermodynamic properties and formation conditions, with a direct impact on emerging hydrate-based technologies.

Confining CO2 inside sI clathrate‐hydrates: The impact of the CO2–water interaction on quantized dynamics

“…The Makov-Payne method of electrostatic interaction correction was considered for these aperiodic systems, where the convergence of the energy is determined by the longest-ranged forces, which usually are electrostatic interactions, evaluated in the limit of large supercells. 87 We used the standard implementation in the LIBXC library, 88 and we choose 27,28,30,31 to employ the PW86PBE functional. Furthermore, as we are dealing with noncovalent systems, we also included dispersion corrections, through the XDM model containing three-body intermolecular dispersion contributions.…”

“…Spectroscopic characterization of CO 2 @sI clathrate hydrates has been reported by solid-state NMR, infrared (IR) and Raman spectroscopy, single crystal X-ray, powder X-ray, and neutron diffraction and scattering experiments, [39][40][41][44][45][46][47][48][49][50][51] while computations from electronic structure quantum chemistry methodologies and molecular dynamics (MD) simulations have investigated guesthost interactions, stability, structural and physical/chemical/ mechanical properties, cage occupancy, phase diagrams, and so forth. 10,13,18,20,23,[27][28][29][30][31]35,[52][53][54][55][56][57] Crystal X-ray and powder X-ray experiments have provided information on the CO 2 orientation in the sI cages, and recorded FTIR/IR spectra have also confirmed the encapsulation of the CO 2 in both small and large sI cages at low temperatures of 5.6 K, providing vibrational transitions of the antisymmetric stretch mode of the 12 CO 2 clathrate and its 13 CO 2 and 18 OCO isotopes, as well as Fermi resonances up to 5100 cm À1 . [39][40][41]49,50 Such findings have clearly indicated the effect of the size, shape and composition of the host-cage on the trapped guest-molecule, and have motivated our previous study 56 on quantum dynamics of a single CO 2 molecule in the sI cages.…”

“…Thus, one way of determining how large such nonadditive contribution could be, is to perform extensive high-level ab initio electronic structure calculations at least for the interactions of the CO 2 molecule with each of the sI cages, and compare them with those from the pairwise representations. Such computations remain still challenging, as a rather high computer resources are demanded, although on the basis of systematic and extensive benchmark studies recently reported, 23,27,28,30,31 density functional theory (DFT) approaches could offer reasonable alternatives. Thus, this study presents the results of our efforts in such directions, through comparisons of the model potentials with DFT-derived interaction energies, and then a very sensitive test of the quality of the PES models through quantum T-R dynamics calculations.…”

“…Clathrate hydrates are crystalline water‐based inclusion compounds with gas molecules trapped in the cavities formed by the ice–water networks. They have been extensively studied due to their technological applications 1–35 . For example, the CO 2 clathrate hydrates are of interest driven by their potential use in CO 2 gas capture and storage from the Earth's atmosphere, and control climate change, 36–38 while in an astrophysical context their formation and presence could influence the composition and stability of planetary ices and comets 39–41 .…”

“…The carbon dioxide clathrate hydrates are known to form crystals of sI structure at low pressures, 41,43 containing small and large cages. Spectroscopic characterization of CO 2 @sI clathrate hydrates has been reported by solid‐state NMR, infrared (IR) and Raman spectroscopy, single crystal X‐ray, powder X‐ray, and neutron diffraction and scattering experiments, 39–41,44–51 while computations from electronic structure quantum chemistry methodologies and molecular dynamics (MD) simulations have investigated guest–host interactions, stability, structural and physical/chemical/mechanical properties, cage occupancy, phase diagrams, and so forth 10,13,18,20,23,27–31,35,52–57 . Crystal X‐ray and powder X‐ray experiments have provided information on the CO 2 orientation in the sI cages, and recorded FTIR/IR spectra have also confirmed the encapsulation of the CO 2 in both small and large sI cages at low temperatures of 5.6 K, providing vibrational transitions of the antisymmetric stretch mode of the clathrate and its and isotopes, as well as Fermi resonances up to 5100 cm −1 39–41,49,50 .…”