Beyer Adrian N, Richardson Jeremy O, Knowles Peter J, Rommel Judith, Althorpe Stuart C
Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
Department of Chemistry, Durham University , South Road, Durham, DH1 3LE, United Kingdom.
J Phys Chem Lett. 2016 Nov 3;7(21):4374-4379. doi: 10.1021/acs.jpclett.6b02115. Epub 2016 Oct 24.
The instanton method obtains approximate tunneling rates from the minimum-action path (known as the instanton) linking reactants to the products at a given temperature. An efficient way to find the instanton is to search for saddle-points on the ring-polymer potential surface, which is obtained by expressing the quantum Boltzmann operator as a discrete path-integral. Here we report a practical implementation of this ring-polymer form of instanton theory into the Molpro electronic-structure package, which allows the rates to be computed on-the-fly, without the need for a fitted analytic potential-energy surface. As a test case, we compute tunneling rates for the benchmark H + CH reaction, showing how the efficiency of the instanton method allows the user systematically to converge the tunneling rate with respect to the level of electronic-structure theory.
瞬子方法在给定温度下从连接反应物和产物的最小作用量路径（即瞬子）获取近似隧穿速率。找到瞬子的一种有效方法是在环聚合物势能面上搜索鞍点，环聚合物势能面是通过将量子玻尔兹曼算符表示为离散路径积分得到的。在此，我们报告了将这种环聚合物形式的瞬子理论实际应用于Molpro电子结构软件包的情况，这使得速率能够即时计算，而无需拟合的解析势能面。作为一个测试案例，我们计算了基准H + CH反应的隧穿速率，展示了瞬子方法的效率如何让用户能够系统地根据电子结构理论水平收敛隧穿速率。
