二维 Nb3Cl8、Nb3Br8 和 Nb3I8 物理性质的第一性原理研究
A first-principles study on the physical properties of two-dimensional Nb3Cl8, Nb3Br8 and Nb3I8
AI总结：
本文通过第一性原理计算系统研究 Nb3Cl8、Nb3Br8 和 Nb3I8 单层的稳定性、剥离能与力学性质，发现三者动力学稳定、易剥离且力学性能随卤素原子量增加而下降。
摘要：
在最近的一项进展中，具有 kagome 晶格和电子拓扑平带的 Nb3Cl8 二维晶体已被实验制备出来（Nano Lett. 2022, 22, 4596）。在受上述进展启发的本工作中，我们开展第一性原理计算，以探究 Nb3X8（X=Cl、Br、I）纳米片的结构、声子色散关系、单层剥离能和力学特征。所得声子色散关系揭示了 Nb3X8（X=Cl、Br、I）单层的动力学稳定性。为了从相应体相材料中分离出单层晶体，我们预测 Nb3Cl8、Nb3Br8 和 Nb3I8 单层的剥离能分别为 0.24、0.27 和 0.28 J/m2，明显低于石墨烯的剥离能。我们发现 Nb3X8 单层是相对坚固的纳米片，具有各向同性弹性和各向异性拉伸强度。此外还表明，随着 Nb3X8 纳米片中卤素原子原子量的增加，其力学特性下降。所呈现的结果为认识 Nb3X8（X=Cl、Br、I）新型二维体系的关键物理性质提供了有益视角。
英文摘要：
In a recent advance, Nb3Cl8 two-dimensional crystals with a kagome lattice and electronic topological flat bands has been experimentally fabricated (Nano Lett. 2022, 22, 4596). In this work motivated by the aforementioned progress, we conduct first-principles calculations to explore the structural, phonon dispersion relations, single-layer exfoliation energies and mechanical features of the Nb3X8 (X=Cl, Br, I) nanosheets. Acquired phonon dispersion relations reveal the dynamical stability of the Nb3X8 (X=Cl, Br, I) monolayers. In order to isolate single-layer crystals from bulk counterparts, we predicted exfoliation energies of 0.24, 0.27 and 0.28 J/m2, for the Nb3Cl8, Nb3Br8 and Nb3I8 monolayers, respectively, which are noticeably lower than that of the graphene. We found that the Nb3X8 monolayers are relatively strong nanosheets with isotropic elasticity and anisotropic tensile strength. It is moreover shown that by increasing the atomic weight of halogen atoms in the Nb3X8 nanosheets, mechanical characteristics decline. Presented results provide a useful vision about the key physical properties of novel 2D systems of Nb3X8 (X=Cl, Br, I).
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