Ruckenstein Eli, Shulgin Ivan L, Shulgin Leonid I
Department of Chemical and Biological Engineering, State University of New York at Buffalo, Amherst, New York 14260, USA. feaeliru@acsu. buffalo.edu
J Phys Chem B. 2007 Jun 28;111(25):7114-21. doi: 10.1021/jp071582a. Epub 2007 Jun 6.
The total interaction energy between two H-bonded water molecules in a condensed phase is composed of a binding energy between them and an energy due to a cooperative effect. An approximate simple expression is suggested for the dependence of the interaction energy between two H-bonded water molecules on the number of neighboring water molecules with which they are H-bonded. Using this expression, the probabilities of breaking a H bond with various numbers of H-bonded neighbors are estimated. These probabilities are used in computer simulations of the breaking of specified fractions of H bonds in an ordinary (hexagonal) ice. A large "piece" of hexagonal ice (up to 8 millions molecules) is built up, and various percentages of H bonds are considered broken. It is shown that 62-63% of H bonds must be broken in order to disintegrate the "piece" of ice into disconnected clusters. This value is only a little larger than the percolation threshold (61%) predicted both by the percolation theory for tetrahedral ice and by simulations in which all H bonds were considered equally probable to be broken. When the percentage of broken bonds is smaller than 62-63%, there is a network of H-bonded molecules which contains the overwhelming majority of water molecules. This result contradicts some models of water which consider that water consists of a mixture of water clusters of various sizes. The distribution of water molecules with unequal probabilities for breaking is compared with the simulation involving equal probabilities for breaking. It was found that in the former case, there is an enhanced number of water monomers without H bonds, that the numbers of 2- and 3-bonded molecules are smaller, and the number of 4-bonded molecules is larger than in the latter case.
凝聚相中两个通过氢键相连的水分子之间的总相互作用能由它们之间的结合能以及协同效应产生的能量组成。针对两个通过氢键相连的水分子之间的相互作用能对与之形成氢键的相邻水分子数量的依赖性，提出了一个近似的简单表达式。利用该表达式，估算了与不同数量氢键相连的相邻分子断开氢键的概率。这些概率被用于计算机模拟普通（六方）冰中特定比例氢键的断裂。构建了一大块六方冰（多达800万个分子），并考虑了不同百分比的氢键断裂情况。结果表明，为了将这块冰分解成不相连的簇，必须有62% - 63%的氢键被破坏。这个值仅比四面体冰的渗流理论以及所有氢键被认为具有同等断裂概率的模拟所预测的渗流阈值（61%）略大一点。当断裂键的百分比小于62% - 63%时，存在一个由氢键相连的分子网络，其中包含绝大多数水分子。这一结果与一些认为水由各种大小的水簇混合物组成的水模型相矛盾。将水分子以不等概率断裂的分布与等概率断裂的模拟进行了比较。结果发现，在前一种情况下，没有氢键的水单体数量增加，有2个和3个氢键的分子数量减少，有4个氢键的分子数量比后一种情况多。
