Guest–Host Interactions in Clathrate Hydrates: Benchmark MP2 and CCSD(T)/CBS Binding Energies of CH₄, CO₂, and H₂S in (H₂O)₂₀Cages

Abstract

We present benchmark binding energies of naturally occurring gas molecules CH 4 , CO 2 , and H 2 S in the small cage, namely, the pentagonal dodecahedron (5 12 ) (H 2 O) 20 , which is one of the constituent cages of the 3 major lattices (structures I, II, and H) of clathrate hydrates. These weak interactions require higher levels of electron correlation and converge slowly with an increasing basis set to the complete basis set (CBS) limit, necessitating the use of large basis sets up to the aug-cc-pV5Z and subsequent correction for basis set superposition error (BSSE). For the host hollow (H 2 O) 20 cages, we have identified a most stable isomer with binding energy of −200.8 ± 2.1 kcal/mol at the CCSD(T)/CBS limit (−199.2 ± 0.5 kcal/mol at the MP2/CBS limit). Additionally, we report converged second order Møller−Plesset (MP2) CBS binding energies for the encapsulation of guests in the (H 2 O) 20 cage of −4.3 ± 0.1 for CH 4 @(H 2 O) 20 , −6.6 ± 0.1 for CO 2 @(H 2 O) 20 , and −8.5 ± 0.1 kcal/mol for H 2 S@(H 2 O) 20 , respectively. For CH 4 @(H 2 O) 20 , exhibiting the weakest encapsulation affinity among the three, we report CCSD(T)/aug-cc-pVTZ binding energies and, based on them, a CCSD(T)/CBS estimate of −4.75 ± 0.1 kcal/mol. To the best of our knowledge, the CCSD(T)/aug-cc-pVTZ calculation for CH 4 @(H 2 O) 20 is the largest one reported to date (168 valence electrons, 1978 basis functions, and the correlation of 84 doubly occupied and 1873 virtual orbitals) and required a scalable implementation of the (T) module on 6144 nodes (350 208 cores) of the "Cori" supercomputer at the National Energy Research Supercomputing Center (NERSC) for a total execution time of 195 min (for the (T) part). These efficient scalable implementations of highly correlated methods offer the capability to obtain long-lasting benchmarks of intermolecular interactions in complex systems. They also provide a path toward parametrizing classical potentials needed to study the dynamical and transport properties in these complex systems as well as assess the accuracy of lower scaling electronic structure methods such as density functional theory (DFT) and MP2 including its spin-biased variants.

q-AQUA: A Many-Body CCSD(T) Water Potential, Including Four-Body Interactions, Demonstrates the Quantum Nature of Water from Clusters to the Liquid Phase

“…We now demonstrate the accuracy and robustness of q-AQUA for standard “stress” tests, namely, the dissociation energies, harmonic frequencies, and diffusion Monte Carlo (DMC) calculations of zero-point energies of isomers of the water hexamer and the dissociation energies of several isomers of the 20-mer, for which benchmark values have recently been reported . We also report molecular dynamics (MD) and path integral molecular dynamics (PIMD) calculations for the radial distribution function (RDF) and MD and semiquantum ring polymer MD (RPMD) calculations of the diffusion constant over a range of temperatures.…”

“…Table shows the binding energies for three isomers of (H 2 O) 20 and compares the benchmark MP2/aV5Z and MP2/CBS calculations with the predictions of q-AQUA and MB-pol. The q-AQUA prediction for the A3 isomer is in good agreement with the MP2/CBS value, whereas the MB-pol value is more than 4 kcal/mol too low.…”

Many-body Δ-Machine Learning brings the accuracy of conventional force field to coupled cluster: application to the TTM2.1 water force field

“…Recently, Heindel et al reported benchmark electronic dissociation energies of several 20mers. 40 This is a stringent test of a FF and this was done for TTM2.1-F and also for the MB-pol FF. For the latter, the energies are roughly 5 kcal/mol lower than the benchmark values.…”

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

“…Finally, the hexagonal sH unit cell is made up of 34 water molecules distributed in three 5 12 , two irregular dodecahedra 4 3 5 6 6 3 (with 20 water molecules) small cages and one large icosahedron 5 12 6 8 (with 36 water molecules) cage. 5,11,12 Less common clathrate hydrates structures, such as the C 0 , C 1 , C 2 , etc. have been also reported.…”

“…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. 8 The stability of these complexes arises from the hydrogen bonds established between water molecules and the van der Waals (vdW) dispersion forces between host and guest species.…”