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arXiv 1004.4294cond-mat.stat-mechnlin.CDphysics.chem-ph
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Hamilton等速恒温器的相空间结构和动力学

Phase space structure and dynamics for the Hamiltonian isokinetic thermostat

Peter Collins, Gregory S. Ezra, Stephen Wiggins

摘要:

我们调查的相空间结构和动力学的哈密顿等速恒温器,遍历恒温器的轨迹在固定(零)的能量产生的配置空间中的正则分布。所研究的模型势由单模和横谐模组成。解释作为一个反应(异构化)坐标的模式,我们建立与理论的单分子反应速率,特别是制定的异构化率的间隙时间。间隔时间(或相关的寿命)的分布为一个微正则系综上的划分表面上发起的是非常重要的动力学意义;指数寿命分布通常被视为是一个指标的“统计”行为。此外,当反应轨迹穿过反应物区域时,它们与反应物区域的总相空间体积(经典态密度)的相空间体积的大小的比较提供了遍历动力学的必要条件。我们计算间隙时间,相关的寿命分布,平均间隙时间,反应通量,反应体积和总反应物相空间体积模型系统与3个自由度,在三个不同的温度。在所有三个温度下,遍历性的必要条件近似满足。在高温下的非指数寿命分布被发现,而在低温下的寿命更接近指数。通过计算纯指数衰减的信息熵亏损来量化寿命分布的指数性程度。的哈密顿等速恒温器的功效检查通过计算平均在分割表面上发起的单个长轨迹的坐标分布。

英文摘要:

We investigate the phase space structure and dynamics of a Hamiltonian isokinetic thermostat, for which ergodic thermostat trajectories at fixed (zero) energy generate a canonical distribution in configuration space. Model potentials studied consist of a single bistable mode plus transverse harmonic modes. Interpreting the bistable mode as a reaction (isomerization) coordinate, we establish connections with the theory of unimolecular reaction rates, in particular the formulation of isomerization rates in terms of gap times. The distribution of gap times (or associated lifetimes) for a microcanonical ensemble initiated on the dividing surface is of great dynamical significance; an exponential lifetime distribution is usually taken to be an indicator of `statistical' behavior. Moreover, comparison of the magnitude of the phase space volume swept out by reactive trajectories as they pass through the reactant region with the total phase space volume (classical density of states) for the reactant region provides a necessary condition for ergodic dynamics. We compute gap times, associated lifetime distributions, mean gap times, reactive fluxes, reactive volumes and total reactant phase space volumes for model systems with 3 degrees of freedom, at three different temperatures. At all three temperatures, the necessary condition for ergodicity is approximately satisfied. At high temperatures a non-exponential lifetime distribution is found, while at low temperatures the lifetime is more nearly exponential. The degree of exponentiality of the lifetime distribution is quantified by computing the information entropy deficit with respect to pure exponential decay. The efficacy of the Hamiltonian isokinetic thermostat is examined by computing coordinate distributions averaged over single long trajectories initiated on the dividing surface.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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