Entropy-driven structures of the water octamer

Pople's Gaussian‐3 model chemistry applied to an investigation of (H2O)8 water clusters

“…To form the cyclic S 8 octamer requires an additional 5.85 kcal/mol of free energy. This result contrasts sharply with previous predictions that the cyclic structure should dominate on the (H 2 O) 8 potential energy hypersurface above 240 K [63,67,118]. Smith et al [118] used B3LYP/6-311ϩϩG** calculations to predict that the S 4 cubic structure was 1.3 kcal/mol higher in free energy than the cyclic structure.…”

“…The D 2d cube is predicted to be completely negligible over the 200 -300 K temperature range, while the cyclic structure is predicted to predominate over all other possible water clusters [117], a commonly accepted view [89,97]. By contrast, Lee et al [93] calculated ⌬G for the formation of water clusters from individual monomers using MP2 theory and large basis sets, and they find the D 2d and S 4 cubes to be significantly more stable than cyclic structures at 50 K. Kim et al [63] used HF and MP2 theory with double zeta plus polarization basis sets to predict that the global minimum octamer is a cube with D 2d symmetry at 0 K, with the S 4 symmetry structure becoming more stable above 40 K, and then the cyclic structure becoming the most stable above 230 K. Smith et al [118] used B3LYP calculations to predict that the cyclic structure has the lowest free energy at room temperature. In the present work, we report stateof-the-art thermodynamic predictions for 18 (H 2 O) 8 structures using the G3 methodology.…”

Small Clusters of Water Molecules Using Density Functional Theory

“…cube. The trilobate structure of symmetry C , when proposed by Stillinger 6b using his polarizable water model, was supposed to be the most stable arrangement of eight water molecules; quantum-mechanical calculations do not support this conclusion: HF/4-31G calculations 48 demonstrated that this structure is not a minimum, while our calculation, HF/DZP 49 and the planewaves-DFT 16 results yield this geometry as a true minimum, but not as the most stable minimum. Nevertheless, this local minimum structure is interesting, since it can be though of having the same structure of an octamer in the hexagonalice lattice.…”

Interaction of oxalic acid with methylamine and its atmospheric implications

“…The total concentrations of oxalic acid and methylamine were selected as 5 Â 10 11 cm À3 and 1 Â 10 7 cm À3 , respectively. 69,73 The concentrations of all the clusters were calculated, and the results are listed in Table 3. It is predicted that the concentration of (H 2 C 2 O 4 )(CH 3 NH 2 ) clusters in the atmosphere is 2.706 Â 10 3 molecules per cm 3 .…”

“…Previous studies 1,72 showed that the energy differences between the global minimum and other local minima become smaller when cluster systems grow larger and their congurations grow more complex. In addition, researchers 72,[73][74][75] also found that the thermodynamic properties and variations in the population order of the isomers could be affected by differences in temperature, which revealed that the temperature dependence of cluster formation is a signicant factor for understanding the nucleation mechanism. However, it is difficult to perform the relevant experiments, i.e., the formation of clusters of oxalic acid with methylamine, at low temperatures owing to wall losses.…”