Density Functional Theory Calculations of Water Fullerenes: (H₂O)_n Clusters with n = 20–40

Water fullerenes (H₂O)_n (n = 20–40) with empty cage configurations were systematically studied by first-principles calculations within gradient corrected density functional theory. The initial configurations were generated from the carbon fullerenes. At each size, the most stable configurations of water fullerenes were selected from the fully optimized structural isomers and the strength of hydrogen bond was discussed in terms of their stabilization energy. There is a correspondence between the relative stability and the O–O distance of water cages. All water fullerene cages considered here, i.e., from (H₂O)₂₀ to (H₂O)₄₀, are locally stable. Even larger (H₂O)_n (n > 30) clusters possess relatively larger stabilization energy per monomer. The optimal configuration of (H₂O)₄₀ fullerene is a tube-like polar cage with exceptional stability, which is different from the other sized water fullerenes of nearly spherical shape.