Effects of the CO2 Guest Molecule on the sI Clathrate Hydrate Structure

Abstract

This paper analyzes the structural, energetic and mechanical properties of carbon dioxide hydrate clathrates calculated using finite cluster and periodic ab initio density-functional theory methodologies. Intermolecular interactions are described by the exchange-hole dipole moment method. The stability, gas saturation energetics, guest–host interactions, cage deformations, vibrational frequencies, and equation of state parameters for the low-pressure sI cubic phase of the CO2@H2O clathrate hydrate are presented. Our results reveal that: (i) the gas saturation process energetically favors complete filling; (ii) carbon dioxide molecules prefer to occupy the larger of the two cages in the sI structure; (iii) blue shifts occur in both the symmetric and antisymmetric stretching frequencies of CO2 upon encapsulation; and (iv) free rotation of guest molecules is restricted to a plane parallel to the hexagonal faces of the large cages. In addition, we calculate the librational frequency of the hindered rotation of the guest molecule in the plane perpendicular to the hexagonal faces. Our calculated spectroscopic data can be used as signatures for the detection of clathrate hydrates in planetary environments.

A Systematic Protocol for Benchmarking Guest–Host Interactions by First‐Principles Computations: Capturing CO2 in Clathrate Hydrates

“…Although several ab initio studies have addressed the intermolecular interactions of H 2 O-H 2 O, CO 2 -H 2 O, and CO 2 -CO 2 complexes, [28][29][30][31][32][33][34] there is little ab initio data on the CO 2 encapsulated in water cages. [35][36][37][38] The lackofabinitio reference computations motivatesu st oc arry out such high quality benchmark data for CO 2 @H 2 Of rom first-principles approaches in sI, sII, and sH type cavities. Computer simulations are ak ey challenge for molecular-level understanding of clathrate behavior,e specially in terms of interpreting the underlying mechanisms of various physicochemical processes (see Ref.…”

“…[39] and references therein). Nowadays, most of the molecular dynamics (MD) simulations still rely on empirical or semiempirical force fields as an important tool for investigating processes, such as the nucleation, growth, structural organization, and cage occupancy of clathrate hydrates, as well as the dissolution of the guest gas in water, [40][41][42][43][44][45][46][47][48][49][50] whereas for ab initio simulations, issues such as computational efficiency,s ystem-size scaling, and accurate electronic structuret reatments are of importance,w ith density functional theory (DFT) approaches [36,38,[51][52][53][54][55] being, more recently,a lso valuable in studyings uch inclusion compounds. In this vein, energy benchmarksf rom accurate quantum-mechanical calculations are essential for testing both force fields and DFT methods.…”

“…Although several ab initio studies have addressed the intermolecular interactions of H 2 O‐H 2 O, CO 2 ‐H 2 O, and CO 2 ‐CO 2 complexes, there is little ab initio data on the CO 2 encapsulated in water cages . The lack of ab initio reference computations motivates us to carry out such high quality benchmark data for CO 2 @H 2 O from first‐principles approaches in sI, sII, and sH type cavities.…”

Characterizing Interstellar Medium, Planetary Surface and Deep Environments by Spectroscopic Techniques Using Unique Simulation Chambers at Centro de Astrobiologia (CAB)

“…During ascent, aqueous fluids under pressure and at low temperatures might take with them clues from the interior environment, while modifying their properties. Examples of these investigations simulating the planetary interior are the characterization of the fractional precipitation and its consequences on the pH of endogenous brines [87], the quantification of the gas solubility in salty aqueous fluids for modelling cryovolcanic processes [88], the determination of the petrological evolution of interesting mineral assemblages and the geological effects on the surface [89], the evaluation of the salting-out caused by gas clathrate crystallization in fluids with salts and gases dissolved [90], or the determination of the guest-effect on high pressure phases of gas clathrates of Ganymede’s and Titan’s oceans [91,92].…”

“…The MPPEC, with a large sapphire window, has allowed to quantify the process, that determine the layering than takes place and to perform a textural analysis of the diverse structures formed. At temperatures down to 267 K, CO 2 -clathrates float over the salty aqueous solution that derives in a later precipitation of hydrated salts [90,91,92,93,94,95,96,97,98]. Figure 7 is a good example of a run performed with respect to this issue.…”