The method of increments is applied to investigate the adsorption of a single water molecule inside and outside armchair carbon nanotubes with different curvature using density-fitting local coupled cluster with single and double excitations and perturbative triples treatment (DF-LCCSD(T)). The correlation contribution to the adsorption energy is expanded in terms of localized orbitals of both the water molecule and the nanotube. Results of this investigation show that the simultaneous correlation of groups of localized orbitals of the water molecule and of the carbon nanotube (i. e. inter-fragment two-body increments) is the major contribution to the attractive interaction. In contrast the individual correlation energy of localized orbitals of water molecule or carbon nanotube (i. e. one-body increments) is negligible. A detailed balance between the repulsive Hartree–Fock contribution and the attractive correlation contribution to the adsorption energy determines the ground-state structure of the water molecule inside the carbon nanotube. To elucidate this behavior benzene-based model systems are investigated with the same methods.
The authors appreciate the support from the FU Focus Area Nanoscale and from the German Research Foundation (DFG) through the Priority Program 1459 (Graphene). The computer facility of the Freie Universität Berlin (ZEDAT) is acknowledged for computer time and support. Helpful discussion with Shujuan Li and PD Dr. Burkhard Schmidt are acknowledged. We also would like to thank Dr. Krista G. Steenbergen, Udbhav Ojha, Matthias Berg and Dr. Carsten Müller for useful discussions.
©2016 Walter de Gruyter Berlin/Boston