Maeda Satoshi, Ohno Koichi
Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
J Phys Chem A. 2007 May 24;111(20):4527-34. doi: 10.1021/jp070606a. Epub 2007 Apr 27.
The potential energy surface (PES) of water octamers has been explored by the scaled hypersphere search method. Among 164 minima on the PES (based on MP2/6-311++G(3df,2p)//B3LYP/6-311+G(d,p) calculations), the cubic structure with D2d symmetry has been confirmed to be the global minimum. In a thermodynamic simulation using these 164 structures, the cubic structure with S4 symmetry has the highest population at low temperature, though double rings can become dominant as temperature going up, in good accord with a recent Monte Carlo simulation using an empirical potential. A transition temperature from cubic to noncubic has significantly been underestimated when potential energy data of B3LYP/6-311+G(d,p) calculations are employed in the simulation. This serious discrepancy between the MP2 and the B3LYP results suggests an importance of dispersion interactions for discussions on thermodynamics of water octamers.
通过缩放超球搜索方法研究了水八聚体的势能面（PES）。在PES上的164个极小值中（基于MP2/6-311++G(3df,2p)//B3LYP/6-311+G(d,p)计算），已证实具有D2d对称性的立方结构是全局最小值。在使用这164种结构的热力学模拟中，具有S4对称性的立方结构在低温下具有最高的丰度，尽管随着温度升高双环可能占主导地位，这与最近使用经验势的蒙特卡罗模拟结果吻合良好。当在模拟中使用B3LYP/6-311+G(d,p)计算的势能数据时，从立方到非立方的转变温度被显著低估。MP2和B3LYP结果之间的这种严重差异表明色散相互作用对于讨论水八聚体的热力学具有重要意义。
