Stable Occupancy of Hydrogen Molecules inH2Clathrate Hydrates andH2+ THF Clathrate Hydrates Determined byAb InitioCalculations

摘要

Structure II clathrate hydrates of pure hydrogen and binary hydrates ofTHF+H2are studied usingab initiocalculations to determine the stable occupancies of small cavities.Ab initiocalculations are carried out for a double cavity consisting of one dodecahedron (small cavity) and one hexakaidecahedron (large cavity). These two cavities are attached to each other as in sII hydrates to form a double cavity. One or twoH2molecules are placed in the small cavity and one THF (or 4H2molecules) molecule is placed in the large cavity. We have determined the binding energies of the double cavities at the MP2 level using various basis sets (3-21G, 3-21G(2p), 3-21++G(2p), 6-31G, 6-31G(2p), and 6-31++G(2p)). Different basis sets yield different stable occupancies of the small cavity. The results from the highest basis set (6-31++G(2p) with zero point energy corrections) indicate that the single occupancy is slightly more favorable than the double occupancy in both the cases of pureH2hydrates and THF +H2double hydrates.