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.