Large local energy fluctuations in water. II. Cooperative motions and fluctuations
Large local energy fluctuations in water. II. Cooperative motions and fluctuations
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水中局部能量波动较大。
DOI：
10.1063/1.455536
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发表时间：
1988
影响因子：
4.4
通讯作者：
P. Wolynes
中科院分区：
文献类型：
--
作者：
I. Ohmine;Hideki Tanaka;P. Wolynes
通过使用经典分子动力学（MD）计算和淬火技术研究液态水中的大局部能量波动及其物理起源。进行100 ps的轨迹计算，发现单个水分子的大旋转运动总是与10-20 kcal/mol的势能不稳定相关，大约每10 ps发生一次。各个水分子的稳定和不稳定是由协同运动引起的。为了分析液态水中的这些协作运动，水结构被淬火到其局部最小值（称为固有结构）。比较系统相继访问的固有结构，发现空间中大约10-40个分子的集体运动发生在不稳定区域。即使在固有结构中，单个分子的势能波动也可达15 kcal/mol。相邻分子之间强烈的势能相关性表明这些协作运动导致了“触发器”型能量交换；当一个分子稳定时，另一个分子就会不稳定，反之亦然。触发器运动不涉及（大的）能量势垒，但会引起单个分子的大能量波动。单个水分子的势能波动的很大一部分被解释为固有结构中的波动和建立在这些结构上的正常模式中的波动的叠加。
Large local energy fluctuations in liquid water and their physical origin are investigated by using classical molecular dynamics (MD) calculation and quenching techniques. Performing a trajectory calculation of 100 ps, it is found that large rotational motions of individual water molecules, which are always associated with potential energy destabilization of 10–20 kcal/mol, occur once in about 10 ps. The stabilization and destabilization of the individual water molecules are induced by cooperative motions. In order to analyze these cooperative motions in the liquid water, the water structures are quenched to their local minima (called the inherent structures). Comparing the inherent structures successively visited by the system, it is found that collective motions of about 10–40 molecules localized in space occur in unstable regions. The potential energy fluctuation of an individual molecule can reach up to 15 kcal/mol even in the inherent structures. The strong potential energy correlation among neighboring molecules indicates these cooperative motions cause the ‘‘flip–flop’’‐type energy exchanges; as a molecule is stabilized, another is to be unstabilized and vice versa. A flip‐flop motion does not involve a (large) energy barrier but causes large energy fluctuations of the individual molecules. A large portion of potential energy fluctuations of the individual water molecules is accounted for as the superposition of fluctuations in the inherent structures and those in the normal modes build upon these structures.