Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
J Chem Phys. 2011 Sep 28;135(12):124109. doi: 10.1063/1.3640429.
We investigate the ability of the recently developed ring-polymer instanton (RPI) method [J. O. Richardson and S. C. Althorpe, J. Chem. Phys. 134, 054109 (2011)] to treat tunneling in water clusters. We show that the RPI method is easy to extend to treat tunneling between more than two minima, using elementary graph theory. Tests of the method on water dimer and trimer yield a set of instanton periodic orbits which correspond to all known tunneling pathways in these systems. Splitting patterns obtained from the orbits are in good overall agreement with experiment. The agreement is closer for the deuterated than for the protonated clusters, almost certainly because the main approximation in the calculations is neglect of anharmonicity perpendicular to the tunneling path. All the calculations were performed on a desktop computer, which suggests that similar calculations will be possible on much larger clusters.
我们研究了最近发展起来的环聚合物瞬时（RPI）方法[J. O. Richardson 和 S. C. Althorpe, J. Chem. Phys. 134, 054109 (2011)]在处理水分子团簇中的隧穿问题的能力。我们表明，使用基本的图论，RPI 方法很容易扩展到处理两个以上势阱之间的隧穿。我们对水分子二聚体和三聚体的方法测试得到了一组瞬时周期轨道，这些轨道对应于这些体系中所有已知的隧穿途径。从轨道中获得的分裂模式与实验总体上吻合良好。对于氘代簇，其吻合程度比对于质子化簇更好，这几乎可以肯定是因为计算中的主要近似是忽略了隧穿路径垂直方向的非谐性。所有的计算都是在台式计算机上进行的，这表明在更大的团簇上进行类似的计算将成为可能。
