First-principles calculation of the thermoelectric figure of merit for [2,2]paracyclophane-based single-molecule junctions
First-principles calculation of the thermoelectric figure of merit for [2,2]paracyclophane-based single-molecule junctions
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DOI：
10.1103/physrevb.91.165419
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发表时间：
2015-04-20
影响因子：
3.7
通讯作者：
Asai, Yoshihiro
中科院分区：
文献类型：
--
作者：
Buerkle, Marius;Hellmuth, Thomas J.;Asai, Yoshihiro
在此，我们对通过基于[2,2]对环芳烷的单分子结的热电输运进行了理论研究。将从密度泛函理论（DFT）获得的电子和振动结构与非平衡格林函数技术相结合，使我们能够在第一性原理层面处理电子和声子的输运性质。对于电子部分，我们基于DFT + Σ方法纳入了一种近似的自能修正。这使我们能够对进入热电优值ZT的所有线性响应输运系数进行可靠预测。对环芳烷衍生物通过连接不同的官能团在调节其化学性质方面具有很大的灵活性。我们表明，对于特定分子，官能团主要影响热电势，使我们能够调节其符号和绝对值。我们预测，对裸对环芳烷进行官能化会大幅提高优值中的电子贡献Z(el)T。然而，声子对热导率的高贡献强烈抑制了ZT。我们的工作表明，对于非共振分子输运结的ZT的任何实际估算，纳入声子热导率都非常重要。此外，它展示了对一系列可用分子的热电性质进行化学调节的可能性，从而基于相同的分子框架产生性能相同的空穴和电子传导结。
Here we present a theoretical study of the thermoelectric transport through [2,2]paracyclophane-based single-molecule junctions. Combining electronic and vibrational structures, obtained from density functional theory (DFT), with nonequilibrium Green's function techniques allows us to treat both electronic and phononic transport properties at a first-principles level. For the electronic part, we include an approximate self-energy correction, based on the DFT+Sigma approach. This enables us to make a reliable prediction of all linear response transport coefficients entering the thermoelectric figure of merit ZT. Paracyclophane derivatives offer a great flexibility in tuning their chemical properties by attaching different functional groups. We show that, for the specific molecule, the functional groups mainly influence the thermopower, allowing us to tune its sign and absolute value. We predict that the functionalization of the bare paracyclophane leads to a largely enhanced electronic contribution Z(el)T to the figure of merit. Nevertheless, the high phononic contribution to the thermal conductance strongly suppresses ZT. Our work demonstrates the importance to include the phonon thermal conductance for any realistic estimate of the ZT for off-resonant molecular transport junctions. In addition, it shows the possibility of a chemical tuning of the thermoelectric properties for a series of available molecules, leading to equally performing hole-and electron-conducting junctions based on the same molecular framework.