The Seebeck coefficient is examined for two-dimensional Dirac electrons in the three-quarter filled organic conductor α-(BEDT-TTF)₂I₃ [BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene] under hydrostatic pressure, where the Seebeck coefficient S is proportional to the ratio of the thermoelectric conductivity L₁₂ to the electrical conductivity L₁₁, i.e., S = L₁₂/TL₁₁ with T being the temperature. We present an improved tight-binding model in two dimensions with transfer energies determined from first-principles density functional theory calculations with an experimentally determined crystal structure. The T dependence of the Seebeck coefficient is calculated by adding impurity and electron–phonon scatterings. Noting a zero-gap state due to the Dirac cone, which results in a competition from contributions between the conduction and valence bands, we show positive S_x and S_y at finite temperatures and analyze them in terms of spectral conductivity. The relevance of the calculated S_x (perpendicular to the molecular stacking axis) to the experiment is discussed.

中文翻译：

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使用源自第一原理的紧束缚模型研究静水压力下有机导体中狄拉克电子的塞贝克效应

检查静水压力下四分之三填充有机导体α -(BEDT-TTF) ₂ I ₃ [BEDT-TTF 表示双(乙撑二硫)四硫富瓦烯]中二维狄拉克电子的塞贝克系数，其中塞贝克系数S为与热电导率L ₁₂与电导率L ₁₁的比值成正比，即S＝L ₁₂ / TL ₁₁其中T为温度。我们提出了一种改进的二维紧束缚模型，其转移能是根据第一原理密度泛函理论计算和实验确定的晶体结构确定的。塞贝克系数的T依赖性是通过添加杂质和电子声子散射来计算的。注意到狄拉克锥导致的零能隙状态，导致导带和价带之间的贡献竞争，我们在有限温度下显示正的S _x和S _y，并根据光谱电导率对它们进行分析。讨论了计算出的S _x（垂直于分子堆积轴）与实验的相关性。