He Inclusion in Ice-like and Clathrate-like Frameworks: A Benchmark Quantum Chemistry Study of Guest–Host Interactions

Energetics and structural properties
of selected type and size
He@hydrate frameworks, e.g., from regular structured ice channels
to clathrate-like cages, are presented from first-principles quantum
chemistry methods. The scarcity of information on He@hydrates makes
such complexes challenging targets, while their computational study
entails an interesting and arduous task. Some of them have been synthesized
in the laboratory, which motivates further investigations on their
stability. Hence, the main focus is to examine the performance and
accuracy of different wave function-based electronic structure methods,
such as MP2, CCSD­(T), their explicitly correlated (F12) and domain-based
local pair-natural orbital (DLPNO) analogs, as well as modern and
conventional density functional theory (DFT) approaches, and analytical
model potentials available. Different structures are considered, starting
from the “simplest system” formed by a noble gas atom
(such as He) and one water molecule, followed by the study of the
“fundamental units” present in all ice-like and clathrate-like
frameworks (such as pentamers and hexamers) and finally the description
of interactions in the “building blocks” of three-dimensional
(3D) ice channels (e.g., horizontal and perpendicular ice II and Ih) and clathrate-like cages, such as the 512 present in the most common sI, sII, and sH clathrate-hydrate
structures. The idea is to provide well-converged DLPNO-CCSD­(T) and
DFMP2/CBS reference datasets that in turn are used to validate how
DFT functionals (in total, 29 approaches from generalized-gradient
approximation (GGA), meta-GGA, to hybrid and range-separated functionals,
including dispersion correction treatments, were checked) and analytical
semiempirical/ab initio-based potentials perform
compared with high-level alternatives. Within all tested approaches,
those best-performing were identified and classified. Most of the
DFT/DFT-D functionals, as well as available analytical pairwise model
potentials, face difficulties in describing both hydrogen-bonded water
frameworks and dispersion bound He–water interactions. Including
dispersion corrections yields an overall well-balanced performance
for LCωPBE-D3BJ and PBE0-D4 functionals. Such benchmark datasets
can benefit research into the development of new cheminformatics models,
as can serve to guide and cross-check methodologies, lending increased
predicted power to future molecular simulations for investigating
the role of structures and phase transitions from nanoscale clusters
to macroscopic crystalline structures.