Integrated ONIOM calculations using the two- and/or three-layer model chemistries were applied to mimic the interaction of water with the basal graphitic layer of HOPG material. The high-level layer in the ONIOM approach is treated at the electron correlated second-order Moller - Plesset perturbation (MP2/6-31G*) level. On the basis of the results obtained, the formation of structural defect sites, molecular and dissociative adsorption complexes of water on a regular and on structural defect sites, the discrepancy in the nature of the surface O - H and C - H groups appeared on SWNT and HOPG materials has been briefly discussed. It was shown that the dissociation of water is highly endothermic on regular sites of HOPG while the energy needed for dissociation decreases substantially if it proceeds on structural defect sites. This finding points out indirectly that the dissociation probability of water increases on SWNT materials as compared to HOPG because of the presence of a larger number of structural defect sites.
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