First principles density functional theory (DFT) with the time-dependent Bethe-Salpeter Equation (BSE) is used to calculate the second harmonic generation (SHG) spectra of five trigonal prismatic (2H-phase) transition metal dichalcogenide (TMD) monolayers, MoS2, MoSe2, WS2, WSe2, and MoTe2, as a function of biaxial and uniaxial strain. It is shown that it is important to take excitonic effects into account when studying the effects of strain on SHG. All the TMDs exhibit very strong SHG, with hexagonal monolayer MoTe2 dominating over the other TMDs in the 0.5-1.4 eV region. These results are shown to agree with experimental data. While WS2 appears to be a good candidate for strain-tolerant applications because the SHG is insensitive to strain, WSe2 exhibits a strong, consistent strain response that points to potential strain-sensitive applications. Distinct subpeaks of the C-exciton are observed which, when compared with the electronic structure, are attributed to specific transitions in the Brillouin zone, with the most important contributions coming from the K (v1 c2), Q(v1 c1), and (v1 c1) points. These findings open new avenues of exploration for potential applications of these materials in strain-sensitive devices and improve our understanding of the C-exciton in TMDs.

中文翻译：

---

过渡金属二硫化氢单层中二次谐波产生的应变依赖性和C激子的精细结构

使用第一原理密度泛函理论（DFT）和随时间变化的Bethe-Salpeter方程（BSE）来计算五个三角棱柱形（2H相）过渡金属二硫化二硅（TMD）单层MoS2的二次谐波生成（SHG）光谱，MoSe2，WS2，WSe2和MoTe2作为双轴和单轴应变的函数。结果表明，在研究菌株对SHG的影响时，必须考虑激子作用。所有TMD都显示出非常强的SHG，在0.5-1.4 eV区域中，六角形单层MoTe2优于其他TMD。这些结果显示与实验数据一致。由于SHG对应变不敏感，而WS2似乎是耐应变应用的良好候选者，而WSe2则显示出强大而一致的应变响应，表明潜在的应变敏感应用。观察到C激子不同的亚峰，与电子结构相比，这归因于布里渊区的特定跃迁，其中最重要的贡献来自K（v1 c2），Q（v1 c1）和（ v1 c1）分。这些发现为这些材料在应变敏感器件中的潜在应用开辟了新的探索途径，并增进了我们对TMD中C激子的理解。