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 make such complexes challenging targets, while their computational study entails an interesting and arduous task. Some of them have been synthesized in the laboratory, that motivates further investigations on their stability. Hence, the main focus is to examine the performance and accuracy of different wavefunction-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 3D ice channels (e.g. horizontal and perpendicular ice II and I h ) and clathrate-like cages, such as the 5 12 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 used to validate how DFT functionals (in total 29 approaches from GGA, meta-GGA, to hybrid and rangeseparated 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 framework and the dispersion bound He-water interaction. Including dispersion corrections yields to an overall well-balance performance for the LCωPBE-D3BJ and PBE0-D4 functionals. Such benchmark datasets can benefit research into the development of new chem-informatics models, as can serve to guide and cross check methodologies, lending 2 increased predicted power to future molecular simulations for investigating the role of structures and phase-transitions from nanoscale clusters to macroscopic crystalline structures.

We performed first-principles computations to investigate guest-host/host-host effects on the encapsulation of the CO 2 molecule in sII clathrate hydrates from finite-size clusters up to periodic 3D crystal lattice systems. Structural and energetic properties were first computed for the individual and first-neighbors clathrate-like sII cages, where highly accurate ab initio quantum chemical methods are available nowadays, allowing in this way the assessment of the density functional (DFT) theoretical approaches employed. 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. On this basis, structural relaxations of the CO 2 -filled and empty sII unit cells yield lattice and compressibility parameters comparable to experimental and previous theoretical values available for sII hydrates. According to these data, the CO 2 enclathration in the sII clathrate cages is a stabilizing process, either by considering both guest-host and host-host interactions in the complete unit cell or only the guest-water energies for the individual clathrate-like sII cages. CO 2 @sII clathrates are predicted to be stable whatever the dispersion correction applied and in the case of single cage occupancy are found to be more stable than the CO 2 @sI structures. Our results reveal that DFT approaches could provide a good reasonable description of the underlying interactions, enabling the investigation of formation and transformation processes as a function of temperature and pressure.

We have assessed the performance and accuracy of different wavefunction-based electronic structure methods, such as DFMP2 and domain-based local pair-natural orbital (DLPNO-CCSD(T)), as well as a variety of density functional...

One of the several possibilities that offer the interesting clathrate hydrates is the opportunity to encapsulate several atoms or molecules, in such a way that more efficient storage materials could...