Non-equilibrium dynamics from RPMD and CMD.
Non-equilibrium dynamics from RPMD and CMD.
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DOI：
10.1063/1.4967958
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发表时间：
2016-11
期刊：
影响因子：
--
通讯作者：
R. Welsch;Kai Song;Qiang Shi;S. Althorpe;Thomas F. Miller
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文献类型：
--
作者：
R. Welsch;Kai Song;Qiang Shi;S. Althorpe;Thomas F. Miller
研究了基于路径积分的两种常用分子动力学方法--环聚合物分子动力学（RPMD）和质心分子动力学（CMD）对近似非平衡态量子时间相关函数（TCF）的计算.结果表明，对于突然的垂直激励和初始动量脉冲的情况下，RPMD和CMD产生非平衡TCF的线性运营商，是准确的高温，在t = 0的限制，和谐波电位;这些条件的子集被保存为非平衡TCF的非线性运营商也进行了讨论。此外，它示出，对于这些非平衡初始条件，这两种方法保留连接到松原动力学，以前已经建立了平衡初始条件。比较非平衡TCFs从RPMD和CMD松原动态在短时间内揭示了该方法同意的时间顺序。具体而言，对于与突然垂直激励相关联的位置自相关函数，RPMD和CMD分别在O（t4）和O（t1）之前与松原动力学一致;对于与初始动量脉冲相关联的位置自相关函数，RPMD和CMD分别在O（t5）和O（t2）之前与松原动力学一致。使用模型势为广泛的非平衡初始条件的数值试验表明，RPMD和CMD产生非平衡TCFs的准确性是可比的平衡TCFs。RPMD也被用来调查激发态质子转移的系统浴模型，它是比较使用最近开发的版本的刘维尔空间层次运动方程的方法进行数值精确计算，再次，类似的精度观察到非平衡和平衡的初始条件。
We investigate the calculation of approximate non-equilibrium quantum time correlation functions (TCFs) using two popular path-integral-based molecular dynamics methods, ring-polymer molecular dynamics (RPMD) and centroid molecular dynamics (CMD). It is shown that for the cases of a sudden vertical excitation and an initial momentum impulse, both RPMD and CMD yield non-equilibrium TCFs for linear operators that are exact for high temperatures, in the t = 0 limit, and for harmonic potentials; the subset of these conditions that are preserved for non-equilibrium TCFs of non-linear operators is also discussed. Furthermore, it is shown that for these non-equilibrium initial conditions, both methods retain the connection to Matsubara dynamics that has previously been established for equilibrium initial conditions. Comparison of non-equilibrium TCFs from RPMD and CMD to Matsubara dynamics at short times reveals the orders in time to which the methods agree. Specifically, for the position-autocorrelation function associated with sudden vertical excitation, RPMD and CMD agree with Matsubara dynamics up to O(t4) and O(t1), respectively; for the position-autocorrelation function associated with an initial momentum impulse, RPMD and CMD agree with Matsubara dynamics up to O(t5) and O(t2), respectively. Numerical tests using model potentials for a wide range of non-equilibrium initial conditions show that RPMD and CMD yield non-equilibrium TCFs with an accuracy that is comparable to that for equilibrium TCFs. RPMD is also used to investigate excited-state proton transfer in a system-bath model, and it is compared to numerically exact calculations performed using a recently developed version of the Liouville space hierarchical equation of motion approach; again, similar accuracy is observed for non-equilibrium and equilibrium initial conditions.