The nonadditive effects in the mixed trimers composed of the water dimer and diatomics H2, HF, HCl, HBr, and ClF

Optimal structures, interaction energies and harmonic vibrational frequencies of the (H2O)2⋯HX, HX=H2, HF, HCl, HBr, and (H2O)2⋯CIF ternary complexes have been determined from the supermolecular MP4 and CCSD(T) calculations with the aug-cc-pVDZ and the aug-cc-pVTZ basis sets. We located three low-energy configurations on the potential energy surface corresponding to H-bonded cyclic complexes and one linear structure in the case of (H2O)2⋯CIF and (H2O)2⋯H2. The tunneling motion of the water molecule across the plane of the heavy atom ring was studied. The contribution of the three-body term represents as much as 24% for (H2O)2⋯HBr and the smallest value of 5% for (H2O)2⋯H2 of the total CCSD(T) interaction energy. The nonadditivity originates mainly from the induction effect.