超低温下Zundel阳离子的会聚色噪声路径积分分子动力学研究
Converged Colored Noise Path Integral Molecular Dynamics Study of the Zundel Cation down to Ultra-low Temperatures at Coupled Cluster Accuracy
摘要：
长期以来，在超低但有限的几开尔文温度下进行收敛路径积分模拟几乎是不可能的任务。然而，最近的发展，先进的色噪声恒温计划的路径积分模拟，即路径积分广义朗之万方程恒温器（PIGLET）和路径积分量子热浴（PIQTB），已经能够大大降低这些模拟的计算成本，从而使超低温制度在实践中获得。在这项工作中，我们调查的影响，这两个恒温方案的氢键系统的描述在温度下降到几个开尔文遇到的，例如，在氦纳米滴隔离或标记光解离光谱实验。为了这个目的，我们分析的原型氢键在Zundel阳离子（H $_5$ O $_{2}^{+}$）作为一个函数，氧-氧距离和温度，以阐明如何各向异性量子离域，因此，共享质子的形状适应取决于供体-受体距离。Zundel阳离子的基本电子结构用Behler神经网络势CCSD（T*）-F12 a/AVTZ描述。此外，性能的PIQTB和PIGLET方法的能量，结构和量子离域属性进行评估和直接比较。总体而言，我们的研究结果强调了这两个现代恒温方法的有效性和实用性的路径积分模拟氢键系统，即使在超低温。
英文摘要：
For a long time, performing converged path integral simulations at ultra-low, but finite temperatures of a few Kelvin has been a nearly impossible task. However, recent developments in advanced colored noise thermostatting schemes for path integral simulations, namely the Path Integral Generalized Langevin Equation Thermostat (PIGLET) and the Path Integral Quantum Thermal Bath (PIQTB), have been able to greatly reduce the computational cost of these simulations, thus making the ultra-low temperature regime accessible in practice. In this work, we investigate the influence of these two thermostatting schemes on the description of hydrogen-bonded systems at temperatures down to a few Kelvin as encountered, for example, in helium nanodroplet isolation or tagging photodissociation spectroscopy experiments. For this purpose, we analyze the prototypical hydrogen bond in the Zundel cation (H$_5$O$_{2}^{+}$) as a function of both, oxygen-oxygen distance and temperature in order to elucidate how the anisotropic quantum delocalization and, thus, the shape of the shared proton adapts depending on the donor-acceptor distance. The underlying electronic structure of the Zundel cation is described in terms of Behler's Neural Network Potentials of essentially converged Coupled Cluster accuracy, CCSD(T*)-F12a/AVTZ. In addition, the performances of the PIQTB and PIGLET methods for energetic, structural, and quantum delocalization properties are assessed and directly compared. Overall, our results emphasize the validity and practical usefulness of these two modern thermostatting approaches for path integral simulations of hydrogen-bonded systems even at ultra-low temperatures.
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