Density functional theoretic studies of host-guest interaction in gas hydrates

Recently we reported the host-guest interaction between a dodecahedral water cage and a variety of guest species that include diatomic (CO, H-2, N-2, O-2), triatomic (CO2, O-3) and polyatomic (CH4, NH3) molecules at the MP2/CBS limit (Kumar and Sathyamurthy, 2011). Since high computational costs involved in the application of MP2 and CCSD (T) methods limit the size of the clathrate that can be studied, the performance of the density functional theoretic method using functionals like B3LYP, M06-HF, M06-L, M06-2X and BLYP-D3 is evaluated for its ability to predict the interaction energy as well as the geometry. The computed results are compared with the estimated CCSD/CBS values, which were obtained with the help of the MP2/CBS values reported earlier. The DFT/BLYP-D3 method seems to be the best; the functionals M06-2X and M06-HF performed reasonably well, while B3LYP failed to predict any attraction between the guest and the host. (C) 2013 Elsevier B.V. All rights reserved.