Table of Contents
Journal of Thermodynamics
Volume 2010 (2010), Article ID 651819, 6 pages
http://dx.doi.org/10.1155/2010/651819
Research Article

Stable Occupancy of Hydrogen Molecules in H 2 Clathrate Hydrates and H 2 + THF Clathrate Hydrates Determined by Ab Initio Calculations

1Department of Chemical Engineering, The City College of the New York, New York, NY 10031, USA
2Department of Chemical and Natural Gas Engineering, Texas A&M University, Kingsville, TX 78363, USA

Received 30 June 2009; Accepted 15 September 2009

Academic Editor: Angelo Lucia

Copyright © 2010 Prasad Yedlapalli et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Structure II clathrate hydrates of pure hydrogen and binary hydrates of T H F + H 2 are studied using ab initio calculations to determine the stable occupancies of small cavities. Ab initio calculations 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 two H 2 molecules are placed in the small cavity and one THF (or 4 H 2 molecules) 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 pure H 2 hydrates and THF + H 2 double hydrates.