论文标题
单分子连接中热传输的模拟：热二极管效应的研究
Simulations of Heat Transport in Single-Molecule Junctions: Investigations of the Thermal Diode Effect
论文作者
论文摘要
为了了解纳米界热能流的微观原理，我们使用经典分子动力学（MD）模拟研究了通过金属 - 分子 - 金属连接的语音热传输。考虑到单分子金烷基硫醇 - 金醇连接，我们首先关注方法开发方面，并比较两种计算热电导的技术：（i）反向非平衡MD（RNEMD）方法，其中热量以相反的金属的恒定速率输入和提取。在这种情况下，由在连接处创建的非平衡温度曲线计算出热电导。 （ii）通过从金属的平衡动力学获得的连接的导热率，接近平衡的MD（AEMD）方法。在这两种方法中，对增长尺寸的烷烃链的模拟都表现出近似于导热电导的长度独立性，并计算出与计算和实验研究相匹配的值。 RNEMD和AEMD方法提供了有关热运输的不同见解，我们讨论了它们的相对好处和缺点。通过评估分子连接作为热二极管的潜在应用，通过使用不同的端群或通过AG替换AG的一个AU接触，通过将其与大块的接触区域修饰与大体进行修饰，在空间不对称上进行空间不对称。非谐性是在分子力场内的系统中内置的。使用RNEMD方法，我们表明，由于这些结构修饰引起的温度曲线差异很大（与金烷基硫醇 - 金连接相比），但在这些系统中，热二极管效应是无关紧要的 - 除非一个人转向非常大的热偏置。这一发现表明，应该寻找具有相当大的内谐作用的分子来开发非线性热设备。
With the objective to understand microscopic principles governing thermal energy flow in nanojunctions, we study phononic heat transport through metal-molecule-metal junctions using classical molecular dynamics (MD) simulations. Considering a single-molecule gold-alkanedithiol-gold junction, we first focus on aspects of method development and compare two techniques for calculating thermal conductance: (i) The Reverse Nonequilibrium MD (RNEMD) method, where heat is inputted and extracted at a constant rate from opposite metals. In this case, the thermal conductance is calculated from the nonequilibrium temperature profile that is created on the junction. (ii) The Approach-to-Equilibrium MD (AEMD) method, with the thermal conductance of the junction obtained from the equilibration dynamics of the metals. In both methods, simulations of alkane chains of growing size display an approximate length-independence of the thermal conductance, with calculated values matching computational and experimental studies. The RNEMD and AEMD methods offer different insights on thermal transport, and we discuss their relative benefits and shortcomings. Assessing the potential application of molecular junctions as thermal diodes, the alkane junctions are made spatially asymmetric by modifying their contact regions with the bulk, either by using distinct endgroups or by replacing one of the Au contacts by Ag. Anharmonicity is built into the system within the molecular force-field. Using the RNEMD method, we show that, while the temperature profile strongly varies (compared to the gold-alkanedithiol-gold junctions) due to these structural modifications, the thermal diode effect is inconsequential in these systems -- unless one goes to very large thermal biases. This finding suggests that one should seek molecules with considerable internal anharmonic effects for developing nonlinear thermal devices.
