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，并在过去的五十年里收集了大量的实验数据。然而，尽管这些数据在定性上得到了理解，但由于缺乏对高压效应进行定量解释的充分理论，所有这些数据都被大大地利用不足。幸运的是，最近计算机技术的进步似乎为解决这一问题提供了适当的工具。通常从过渡态(过渡态)的性质来讨论反应机理，反应物通过这些过渡态转化为产物。传统上，实验测量的压力对反应速率的影响是用所谓的活化体积来表示的，活化体积代表过渡态和反应物的体积之差。由于反应物的体积很容易通过实验获得，因此活化体积提供了过渡态体积的直接测量，从而提供了对这些瞬时物种的独特一瞥。因此，我们提出了一种计算活化量的新方法。在我们的方法中，微观反应体系的体积被确定为体系在溶剂中的阿基米德置换体积，并且被发现是纯溶剂(N个粒子)和含有该体系的溶剂(N+1个粒子)的体积之差。初步计算结果表明，计算体积精度较高。

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.