瞬子理论的双能级方法
Dual-Level Approach to Instanton Theory
摘要：
瞬子理论是计算包括原子隧穿在内的化学反应速率常数的一种成熟方法。技术和方法的改进提高了其适用性。尽管如此，大量的能量和梯度计算是必要的，以优化瞬子隧穿路径和2 $^{\text{nd}}$衍生物的势能沿隧穿路径进行评估，限制了范围内的合适的电子结构的方法。为了提高瞬子理论的适用性，我们提出了一个双水平的方法，其中瞬子优化和海森计算使用一个有效的，但近似的电子结构方法和势能沿隧穿路径重新计算使用更准确的方法。这一过程扩展了瞬子理论的适用性，高层次的电子结构的方法，分析梯度可能无法使用，如本地线性标度的方法。我们演示了分析Eckart势垒和三个分子系统如何双能级瞬子的方法校正的最大部分的错误所造成的不准确的有效的电子结构的方法。这大大减少了计算速率常数的误差。
英文摘要：
Instanton theory is an established method to calculate rate constants of chemical reactions including atom tunneling. Technical and methodological improvements increased its applicability. Still, a large number of energy and gradient calculations is necessary to optimize the instanton tunneling path and 2$^{\text{nd}}$ derivatives of the potential energy along the tunneling path have to be evaluated, restricting the range of suitable electronic structure methods. To enhance the applicability of instanton theory, we present a dual-level approach in which instanton optimizations and Hessian calculations are performed using an efficient but approximate electronic structure method and the potential energy along the tunneling path is recalculated using a more accurate method. This procedure extends the applicability of instanton theory to high-level electronic structure methods for which analytic gradients may not be available, like local linear-scaling approaches. We demonstrate for the analytical Eckart barrier and three molecular systems how the dual-level instanton approach corrects for the largest part of the error caused by the inaccuracy of the efficient electronic structure method. This reduces the error of the calculated rate constants significantly.
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