Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
J Chem Phys. 2018 Jun 21;148(23):234102. doi: 10.1063/1.5029258.
We report an improved method for the calculation of tunneling splittings between degenerate configurations in molecules and clusters using path-integral molecular dynamics (PIMD). Starting from an expression involving a ratio of thermodynamic density matrices at the bottom of the symmetric wells, we use thermodynamic integration with molecular dynamics simulations and a Langevin thermostat to compute the splittings stochastically. The thermodynamic integration is performed by sampling along the semiclassical instanton path, which provides an efficient reaction coordinate as well as being physically well-motivated. This approach allows us to carry out PIMD calculations of the multi-well tunneling splitting pattern in the water dimer and to refine previous PIMD calculations for one-dimensional models and malonaldehyde. The large (acceptor) splitting in the water dimer agrees to within 20% of benchmark variational results, and the smaller splittings agree to within 10%.
我们报告了一种改进的方法，用于使用路径积分分子动力学（PIMD）计算分子和团簇中简并构型之间的隧道分裂。从涉及对称阱底部热力学密度矩阵比的表达式开始，我们使用热力学积分和分子动力学模拟以及朗之万热库来随机计算分裂。热力学积分通过沿着半经典瞬子路径进行采样来完成，该路径提供了有效的反应坐标，并且具有很好的物理基础。这种方法允许我们对水分子二聚体的多阱隧道分裂模式进行 PIMD 计算，并改进以前用于一维模型和丙二醛的 PIMD 计算。水分子二聚体中的大（受体）分裂与基准变分结果的偏差在 20%以内，较小的分裂偏差在 10%以内。
