Pérez Alejandro, Tuckerman Mark E, Müser Martin H
Department of Chemistry, New York University, New York, New York 10003, USA.
J Chem Phys. 2009 May 14;130(18):184105. doi: 10.1063/1.3126950.
The problems of ergodicity and internal consistency in the centroid and ring-polymer molecular dynamics methods are addressed in the context of a comparative study of the two methods. Enhanced sampling in ring-polymer molecular dynamics (RPMD) is achieved by first performing an equilibrium path integral calculation and then launching RPMD trajectories from selected, stochastically independent equilibrium configurations. It is shown that this approach converges more rapidly than periodic resampling of velocities from a single long RPMD run. Dynamical quantities obtained from RPMD and centroid molecular dynamics (CMD) are compared to exact results for a variety of model systems. Fully converged results for correlations functions are presented for several one dimensional systems and para-hydrogen near its triple point using an improved sampling technique. Our results indicate that CMD shows very similar performance to RPMD. The quality of each method is further assessed via a new chi(2) descriptor constructed by transforming approximate real-time correlation functions from CMD and RPMD trajectories to imaginary time and comparing these to numerically exact imaginary time correlation functions. For para-hydrogen near its triple point, it is found that adiabatic CMD and RPMD both have similar chi(2) error.
在对质心和环聚合物分子动力学方法的比较研究背景下，探讨了这两种方法中的遍历性和内部一致性问题。环聚合物分子动力学（RPMD）中的增强采样是通过首先进行平衡路径积分计算，然后从选定的、随机独立的平衡构型启动RPMD轨迹来实现的。结果表明，这种方法比从单个长时间RPMD运行中对速度进行周期性重采样收敛得更快。将从RPMD和质心分子动力学（CMD）获得的动力学量与各种模型系统的精确结果进行了比较。使用改进的采样技术，给出了几个一维系统以及接近三相点的对氢的关联函数的完全收敛结果。我们的结果表明，CMD的性能与RPMD非常相似。通过一种新的χ²描述符进一步评估了每种方法的质量，该描述符是通过将CMD和RPMD轨迹的近似实时关联函数转换为虚时间，并将这些函数与数值精确的虚时间关联函数进行比较而构建的。对于接近三相点的对氢，发现绝热CMD和RPMD具有相似的χ²误差。
