基于Onsager-Machlup action的多尺度增强路径采样：在模型聚合物中的应用
Multiscale enhanced path sampling based on the Onsager-Machlup action: Application to a model polymer
摘要：
我们提出了一种新的路径采样方法的基础上的Onsager-Machlup（OM）的行动，通过推广的多尺度增强采样（MSES）技术提出的Moritsugu和同事（J.化学物理133，224105（2010））。这种方法的基本思想是，我们想要研究的系统（例如，分子力学描述的一些分子系统）被耦合到一个粗粒度（CG）系统，该系统可以比原始系统移动得更快，计算效率更高。我们模拟这个组合系统（原始+ CG系统）使用（欠阻尼）Langevin动力学不同的热浴耦合到两个系统。当耦合足够强时，原系统在CG系统的引导下，能够更有效地对位形和路径空间进行采样。然而，我们需要通过使用哈密顿副本交换来校正由耦合引起的偏差，其中我们制备了具有不同耦合强度的多个路径副本。其结果是，一个无偏的路径合奏的原始系统中可以找到最弱的耦合路径合奏。这种策略很容易实现，因为如果我们正确定义路径的“哈密顿量”，则由OM作用计算的路径的权重在形式上与玻尔兹曼权重相同。我们将这种方法应用于一个具有Asakura-Oosawa相互作用的模型聚合物，并与传统的过渡路径采样方法的结果进行了比较。
英文摘要：
We propose a novel path sampling method based on the Onsager-Machlup (OM) action by generalizing the multiscale enhanced sampling (MSES) technique suggested by Moritsugu and coworkers (J. Chem. Phys. 133, 224105 (2010)). The basic idea of this method is that the system we want to study (for example, some molecular system described by molecular mechanics) is coupled to a coarse-grained (CG) system, which can move more quickly and computed more efficiently than the original system. We simulate this combined system (original + CG system) using (underdamped) Langevin dynamics where different heat baths are coupled to the two systems. When the coupling is strong enough, the original system is guided by the CG system, and able to sample the configuration and path space more efficiency. We need to correct the bias caused by the coupling, however, by employing the Hamiltonian replica exchange where we prepare many path replica with different coupling strengths. As a result, an unbiased path ensemble for the original system can be found in the weakest coupling path ensemble. This strategy is easily implemented because a weight for a path calculated by the OM action is formally the same as the Boltzmann weight if we properly define the path "Hamiltonian". We apply this method to a model polymer with Asakura-Oosawa interaction, and compare the results with the conventional transition path sampling method.
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