How to remove the spurious resonances from ring polymer molecular dynamics
How to remove the spurious resonances from ring polymer molecular dynamics
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DOI：
10.1063/1.4883861
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发表时间：
2014-06-21
影响因子：
4.4
通讯作者：
Manolopoulos, David E.
中科院分区：
文献类型：
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作者：
Rossi, Mariana;Ceriotti, Michele;Manolopoulos, David E.
质心分子动力学（CMD）和环聚合物分子动力学（RPMD）是目前用于模拟凝聚相体系量子动力学的两种最成功的方法。尽管它们的概念差异，这些方法的实际实施仅在两个方面有所不同：选择的Parrinello-Rahman质量矩阵和是否恒温器是应用于内部模式的环聚合物在动态。在这里，我们探索一种方法，这是中间的两个近似：我们保持路径积分珠质量等于物理粒子质量，但附加一个朗之万恒温器的内部模式的环聚合物在动态。我们证明这一点，分析表明，包括一个内部模式恒温器不影响任何既定的功能RPMD：恒温RPMD是同样有效的，相对于一切，实际上已经证明了有关的方法作为RPMD本身。特别是，由于珠质量的选择，所得到的方法仍然是最佳的在短时间内的限制，和过渡态近似的反应速率理论仍然密切相关的半经典瞬子近似在深量子隧道制度。实际上，有一个连续的家庭的方法与这些属性，参数化的强度朗之万摩擦。在这里，我们探讨数值近似量子动力学如何依赖于这种摩擦，特别强调振动光谱。我们发现，一个广泛的摩擦接近最佳阻尼给出类似的结果，这些结果是免疫RPMD的共振问题和CMD的曲率问题。(C)2014 AIP Publishing LLC.
Two of the most successful methods that are presently available for simulating the quantum dynamics of condensed phase systems are centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD). Despite their conceptual differences, practical implementations of these methods differ in just two respects: the choice of the Parrinello-Rahman mass matrix and whether or not a thermostat is applied to the internal modes of the ring polymer during the dynamics. Here, we explore a method which is halfway between the two approximations: we keep the path integral bead masses equal to the physical particle masses but attach a Langevin thermostat to the internal modes of the ring polymer during the dynamics. We justify this by showing analytically that the inclusion of an internal mode thermostat does not affect any of the established features of RPMD: thermostatted RPMD is equally valid with respect to everything that has actually been proven about the method as RPMD itself. In particular, because of the choice of bead masses, the resulting method is still optimum in the short-time limit, and the transition state approximation to its reaction rate theory remains closely related to the semiclassical instanton approximation in the deep quantum tunneling regime. In effect, there is a continuous family of methods with these properties, parameterised by the strength of the Langevin friction. Here, we explore numerically how the approximation to quantum dynamics depends on this friction, with a particular emphasis on vibrational spectroscopy. We find that a broad range of frictions approaching optimal damping give similar results, and that these results are immune to both the resonance problem of RPMD and the curvature problem of CMD. (C) 2014 AIP Publishing LLC.