Chen Renai, Dinpajooh Mohammadhasan, Nitzan Abraham
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA.
J Chem Phys. 2023 Oct 7;159(13). doi: 10.1063/5.0168117.
Classical molecular dynamics (MD) has been shown to be effective in simulating heat conduction in certain molecular junctions since it inherently takes into account some essential methodological components which are lacking in the quantum Landauer-type transport model, such as many-body full force-field interactions, anharmonicity effects and nonlinear responses for large temperature biases. However, the classical MD reaches its limit in the environments where the quantum effects are significant (e.g. with low-temperatures substrates, presence of extremely high frequency molecular modes). Here, we present an atomistic simulation methodology for molecular heat conduction that incorporates the quantum Bose-Einstein statistics into an "effective temperature" in the form of a modified Langevin equation. We show that the results from such a quasi-classical effective temperature MD method deviates drastically when the baths temperature approaches zero from classical MD simulations and the results converge to the classical ones when the bath approaches the high-temperature limit, which makes the method suitable for full temperature range. In addition, we show that our quasi-classical thermal transport method can be used to model the conducting substrate layout and molecular composition (e.g. anharmonicities, high-frequency modes). Anharmonic models are explicitly simulated via the Morse potential and compared to pure harmonic interactions to show the effects of anharmonicities under quantum colored bath setups. Finally, the chain length dependence of heat conduction is examined for one-dimensional polymer chains placed in between quantum augmented baths.
经典分子动力学（MD）已被证明在模拟某些分子结中的热传导方面是有效的，因为它本质上考虑了量子朗道尔型输运模型中缺乏的一些基本方法学要素，例如多体全力场相互作用、非谐效应以及大温度偏置下的非线性响应。然而，在量子效应显著的环境中（例如低温基板、存在极高频率分子模式），经典分子动力学达到了其极限。在此，我们提出一种用于分子热传导的原子模拟方法，该方法将量子玻色 - 爱因斯坦统计以修正朗之万方程的形式纳入“有效温度”。我们表明，当浴温从经典分子动力学模拟接近零时，这种准经典有效温度分子动力学方法的结果会大幅偏离，而当浴温接近高温极限时，结果会收敛到经典结果，这使得该方法适用于全温度范围。此外，我们表明我们的准经典热输运方法可用于模拟导电基板布局和分子组成（例如非谐性、高频模式）。通过莫尔斯势明确模拟非谐模型，并与纯谐相互作用进行比较，以展示在量子色浴设置下非谐性的影响。最后，研究了置于量子增强浴之间的一维聚合物链的热传导对链长的依赖性。
