Thesis (M.Sc.)--Chulalongkorn University, 2007

Optimal binding sites and the corresponding binding energies between CH[subscript 4] molecules and three type of IRMOF namely IRMOF-1, IRMOF-6 and IRMOF-14. The IRMOF structures were optimized using the DFT calculation with the 6-31G** basis set. The clusters were validated using three different sizes of IRMOF clusters, SINGLE, DOUBLE and TRIPLE. CH[subscript 4] molecules were assigned to approach the linker (LINK) and corner (CORN) domains of the clusters in the H-in and H-out configulations. The ONIOM(MP2/6-31G**:HF/6-31G**) with the corrections due to the basis set superposition errors was found to be the optimal choice for the investigated systems. Among the three cluster sized, SINGLE cluster is sufficient to represent interactions with CH[subscript 4]. The optimal binding sites of CH[subscript 4] molecules as well as their orientations in the cavity of the IRMOFs are CORN (H-out) for IRMOF-1 and IRMOF-6 with the corresponding binding energies of -3.64 and -3.53 kJ/mol, respectively. The corresponding binding energies for IRMOF-14 is -3.77 kJ/mol in the H-in configulation at LINK domaim.