On the stability of dense versus cage-shaped water clusters:: Quantum-chemical investigations of zero-point energies, free energies, basis-set effects and IR spectra of (H2O)12 and (H2O)20

The energetics of water clusters with 12 and 20 molecules are studied by quantum-chemical computations using the 133LYP, MP2, MP4 and CCSD methods. The effect of electron-correlation method, basis set, zero-point energy, thermal energy and Gibbs free energy on the relative stability of fused clusters (structures consisting of cubic- or prismatic-shaped subparts) versus cage-shaped clusters (more open structures with only three-coordinated molecules) are investigated. The O-H stretching IR vibrational spectra are studied. The contribution of zero-point and Gibbs free energy will diminish the energy difference between fused- and cage-shaped clusters, but the fused structures are still slightly more favorable. (c) 2005 Elsevier B.V. All rights reserved.