Fragmentation of water clusters: Molecular-dynamics simulation study

Global Search for Minimum Energy (H2O)n Clusters, n = 3−5

“…The structure of the water trimer minimum is identical to previous electronic structure results. ,,,,− ,,,,,,,,− ,,,, While the cyclic trimer is clearly the experimental global minimum at low temperatures, , other calculated trimer structures have been reported. Empirical force fields lead to more minima than just the cyclic structure, ,,, as do quantum chemical calculations at lower levels of theory. ,, Wang and Gunn have used a semiempirical valence bond approach to locate four equilibrium structures of water trimers . Besides the cyclic minima, they found two linear structures and a different cyclic structure than we located.…”

“…As shown in Figure , the four tetramers include two cyclic structures that have been described before using empirical potentials and ab initio chemistry, with S 4 ,,,,,,,,, and C i 27 symmetry, and two additional structures described as a pyramid 27,31 and a lasso. , An additional structure that we did not find through our conformational search was the 2DD2AA structure, displayed in Figure . We located 10 pentamers, the cyclic structure that has been reported previously, ,,,,,,,,− , and the 9 additional structures displayed in Figure . Five of these consist of fused rings, and the other four are cagelike structures.…”

“…This structure has an electronic energy 0.08 kcal/mol higher than the minimum that has one hydrogen on the opposite side of the cyclic plane relative to the other two hydrogens. As shown in Figure 1, the four tetramers include two cyclic structures that have been described before using empirical potentials and ab initio chemistry, with S 4 4,5,23,27,28,31,32,36,63,64 and C i 27 symmetry, and two additional structures described as a pyramid 27,31 and a lasso. 5,32 An additional structure that we did not find through our conformational search was the 2DD2AA structure, displayed in Figure 1.…”

“…Numerous experimental and theoretical studies have focused on understanding the structure of small water clusters, (H 2 O) n , with n = 3−5. − We have recently predicted that besides the water dimer, the cyclic trimer, cyclic tetramer, and cyclic pentamer are also present in the earth's lower atmosphere under humid conditions. , A recent study of the atmosphere in the near-infrared has revealed that the water dimer is present at a temperature of 292.4 K . This study suggests that the water dimer concentration is approximately 6 × 10 14 molecules/cm 3 for saturated air at 292.4 K. We have recently used model chemistry methods − to predict the concentration of the water dimer and other cyclic water clusters where n = 2−6 .…”

“…2,5,7,9,[16][17][18]21,23,29,30,32,34,36,[40][41][42]47,49,63,64 While the cyclic trimer is clearly the experimental global minimum at low temperatures, 16,42 other calculated trimer structures have been reported. Empirical force fields lead to more minima than just the cyclic structure, 2,5,14,31 as do quantum chemical calculations at lower levels of theory. 19,23,27 Wang and Gunn have used a semiempirical valence bond approach to locate four equilibrium structures of water trimers.…”