Molecular dynamics of high pressure reactions in condensed

压力是决定化学反应选择性、方向和速率的重要物理参数。压力对化学动力学的影响得到了很好的研究，在过去的五十年中收集了大量的实验数据。然而，尽管从质量上理解了这些数据，但由于缺乏定量解释高压效应的适当理论，所有这些数据都没有得到充分利用。幸运的是，最近计算机技术的进步似乎为解决这个问题提供了合适的工具。反应机理通常根据瞬态（过渡态）的性质来讨论，通过这些性质，反应物转变为产物。传统上，实验测量的压力对反应速率的影响是用所谓的激活体积来表示的，它代表了过渡态和反应物体积的差异。由于反应物的体积在实验上很容易得到，激活体积提供了过渡态体积的直接测量，从而对这些瞬态物质有了独特的了解。我们提出了一种计算活化体积的新方法。在我们的方法中，微观反应系统的体积被确定为系统在溶剂中的阿基米德位移体积，并被发现为纯溶剂（N个粒子）和含有系统的溶剂（N+1个粒子）的体积之差。初步结果表明，计算体积具有较高的精度。

Pressure is an important physical parameter that determines selectivity, direction, and rates of chemical reactions. The effects of pressure on chemical kinetics are well studied and a vast amount of experimental data has been collected over the last fifty years. However, although they are qualitatively understood, all these data are greatly underutilized because of the lack of an adequate theory that accounts quantitatively for high-pressure effects. Fortunately, the recent advancement of computer technology seems to provide a proper instrument for tackling this problem.    Reaction mechanisms are usually discussed in terms of properties of transient states (transition states), through which reactants transform into products. Traditionally, the experimentally measured effects of pressure on reaction rates are expressed in terms of so-called volumes of activation, which represent the difference in volumes of transition states and reactants. Since the volumes of reactants are readily available experimentally, the volumes of activation provide a direct measure of the transition state volumes and thus a unique glimpse at these transient species.    We propose a new method for calculating activation volumes. Within our approach, the volume of a microscopic reaction system is determined as an Archimedean displacement volume of the system in a solvent and is found as a difference between the volumes of the pure solvent (N particles) and the solvent containing the system (N+1 particles). Preliminary results indicate that the volumes can be calculated with high precision.