Appropriate description of intermolecular interactions in the methane hydrates: An assessment of DFT methods

Accurate description of hydrogen‐bonding energies between water molecules and van der Waals interactions between guest molecules and host water cages is crucial for study of methane hydrates (MHs). Using high‐level ab initio MP2 and CCSD(T) results as the reference, we carefully assessed the performance of a variety of exchange–correlation functionals and various basis sets in describing the noncovalent interactions in MH. The functionals under investigation include the conventional GGA, meta‐GGA, and hybrid functionals (PBE, PW91, TPSS, TPSSh, B3LYP, and X3LYP), long‐range corrected functionals (ωB97X, ωB97, LC‐ωPBE, CAM‐B3LYP, and LC‐TPSS), the newly developed Minnesota class functionals (M06‐L, M06‐HF, M06, and M06‐2X), and the dispersion‐corrected density functional theory (DFT) (DFT‐D) methods (B97‐D, ωB97X‐D, PBE‐TS, PBE‐Grimme, and PW91‐OBS). We found that the conventional functionals are not suitable for MH, notably, the widely used B3LYP functional even predicts repulsive interaction between CH4 and (H2O)6 cluster. M06‐2X is the best among the M06‐Class functionals. The ωB97X‐D outperforms the other DFT‐D methods and is recommended for accurate first‐principles calculations of MH. B97‐D is also acceptable as a compromise of computational cost and precision. Considering both accuracy and efficiency, B97‐D, ωB97X‐D, and M06‐2X functional with 6‐311++G(2d,2p) basis set without basis set superposition error (BSSE) correction are recommended. Though a fairly large basis set (e.g., aug‐cc‐pVTZ) and BSSE correction are necessary for a reliable MP2 calculation, DFT methods are less sensitive to the basis set and BSSE correction if the basis set is sufficient (e.g., 6‐311++G(2d,2p)). These assessments provide useful guidance for choosing appropriate methodology of first‐principles simulation of MH and related systems. © 2012 Wiley Periodicals, Inc.