Avdoshenko Stanislav M, Makarov Dmitrii E
Institute for Computational Engineering and Sciences, University of Texas at Austin, Austin, Texas 78712, USA.
J Chem Phys. 2015 May 7;142(17):174106. doi: 10.1063/1.4919541.
In covalent mechanochemistry, precise application of mechanical stress to molecules of interest ("mechanophores") is used to induce to promote desired reaction pathways. Computational prediction of such phenomena and rational mechanophore design involves the computationally costly task of finding relevant transition-state saddles on force-deformed molecular potential energy surfaces (PESs). Finding a transition state often requires an initial guess about the pathway by which the reaction will proceed. Unfortunately, chemical intuition often fails when predicting likely consequences of mechanical stress applied to molecular systems. Here, we describe a fully deterministic method for finding mechanochemically relevant transition states and reaction pathways. The method is based on the observation that application of a sufficiently high mechanical force will eventually destabilize any molecular structure. Mathematically, such destabilization proceeds via a "catastrophe" occurring at a critical force where the energy minimum corresponding to the stable molecular structure coalesces with a transition state. Catastrophe theory predicts the force-deformed PES to have universal behavior in the vicinity of the critical force, allowing us to deduce the molecular structure of the transition state just below the critical force analytically. We then use the previously developed method of tracking transition-state evolution with the force to map out the entire reaction path and to predict the complete force dependence of the reaction barrier. Beyond its applications in mechanochemistry, this approach may be useful as a general method of finding transition states using fictitious forces to target specific reaction mechanisms.
在共价机械化学中，对感兴趣的分子（“机械力发色团”）精确施加机械应力，用于诱导和促进所需的反应途径。对此类现象的计算预测和合理的机械力发色团设计，涉及在力变形分子势能面（PES）上寻找相关过渡态鞍点这一计算成本高昂的任务。找到一个过渡态通常需要对反应将进行的途径有一个初始猜测。不幸的是，在预测施加于分子系统的机械应力可能产生的后果时，化学直觉常常失灵。在此，我们描述一种用于找到与机械化学相关的过渡态和反应途径的完全确定性方法。该方法基于这样的观察：施加足够高的机械力最终会使任何分子结构变得不稳定。从数学上讲，这种不稳定通过在临界力处发生的“突变”来进行，此时对应于稳定分子结构的能量最小值与一个过渡态合并。突变理论预测力变形的PES在临界力附近具有普遍行为，这使我们能够解析地推断出略低于临界力的过渡态的分子结构。然后，我们使用先前开发的随力跟踪过渡态演化的方法，来描绘出整个反应路径，并预测反应势垒对力的完全依赖性。除了其在机械化学中的应用，这种方法作为一种使用虚拟力来针对特定反应机制寻找过渡态的通用方法可能会很有用。
