Collepardo-Guevara Rosana, Suleimanov Yury V, Manolopoulos David E
Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, United Kingdom.
J Chem Phys. 2009 May 7;130(17):174713. doi: 10.1063/1.3127145.
We describe an efficient procedure for calculating the rates of bimolecular chemical reactions in the gas phase within the ring polymer molecular dynamics approximation. A key feature of the procedure is that it does not require that one calculate the absolute quantum mechanical partition function of the reactants or the transition state: The rate coefficient only depends on the ratio of these two partition functions which can be obtained from a thermodynamic integration along a suitable reaction coordinate. The procedure is illustrated with applications to the three-dimensional H + H(2), Cl + HCl, and F + H(2) reactions, for which well-converged quantum reactive scattering results are computed for comparison. The ring polymer rate coefficients agree with these exact results at high temperatures and are within a factor of 3 of the exact results at temperatures in the deep quantum tunneling regime, where the classical rate coefficients are too small by several orders of magnitude. This is probably already good enough to encourage future applications of the ring polymer theory to more complex chemical reactions, which it is capable of treating in their full dimensionality. However, there is clearly some scope for improving on the ring polymer approximation at low temperatures, and we end by suggesting a way in which this might be accomplished.
我们描述了一种在环聚合物分子动力学近似下计算气相中双分子化学反应速率的有效方法。该方法的一个关键特征是，它不需要计算反应物或过渡态的绝对量子力学配分函数：速率系数仅取决于这两个配分函数的比值，而这可以通过沿着合适的反应坐标进行热力学积分得到。通过将该方法应用于三维H + H₂、Cl + HCl和F + H₂反应进行了说明，为了进行比较，计算了收敛良好的量子反应散射结果。环聚合物速率系数在高温下与这些精确结果一致，在深量子隧穿区域的温度下，与精确结果相差不超过3倍，而经典速率系数则小几个数量级。这可能已经足以鼓励未来将环聚合物理论应用于更复杂的化学反应，该理论能够在其全维度下处理这些反应。然而，在低温下改进环聚合物近似显然还有一定空间，我们最后提出了一种可能实现这一目标的方法。
