二维过渡金属二硫族化合物的晶体场、配位场和轨道间效应
Crystal field, ligand field, and interorbital effects in two-dimensional transition metal dichalcogenides across the periodic table
摘要：
二维过渡金属二硫属化物（TMD）以两种多晶型存在，称为$1T$和$1H$，这取决于过渡金属原子的配位范围。八面体和三角棱柱对称性的破坏导致了$d$电子态的不同晶体和配体场分裂，从而导致了不同的电子性质。在这项工作中，我们量化的晶体和配位场参数的二维TMD使用Wannier函数的方法。我们采用Scaramucci et al. [A. Scaramucci等人，J.物理学：康登斯Matter 27，175503（2015）]。通过在Wannier函数的构造中选择不同的流形，可以分离对配体场的各种贡献。我们讨论的晶体和配位场的相关性，在确定两种多晶型物的相对稳定性作为填充的$d$ -壳的函数。基于计算的参数，我们得出结论，配位场，而导致一个小的稳定因子的$1H$多晶型物中的$d^1$和$d^2$ TMD，主要起着间接的作用，不同的$d$轨道之间的杂交是占主导地位的功能。我们调查整个周期表的趋势，并解释计算的晶体和配体场的变化方面的电荷转移能量的变化，这使得开发简单的化学直觉。
英文摘要：
Two-dimensional transition metal dichalcogenides (TMDs) exist in two polymorphs, referred to as $1T$ and $1H$, depending on the coordination sphere of the transition metal atom. The broken octahedral and trigonal prismatic symmetries lead to different crystal and ligand field splittings of the $d$ electron states, resulting in distinct electronic properties. In this work, we quantify the crystal and ligand field parameters of two-dimensional TMDs using a Wannier-function approach. We adopt the methodology proposed by Scaramucci et al. [A. Scaramucci et al., J. Phys.: Condens. Matter 27, 175503 (2015)]. that allows to separate various contributions to the ligand field by choosing different manifolds in the construction of the Wannier functions. We discuss the relevance of the crystal and ligand fields in determining the relative stability of the two polymorphs as a function of the filling of the $d$-shell. Based on the calculated parameters, we conclude that the ligand field, while leading to a small stabilizing factor for the $1H$ polymorph in the $d^1$ and $d^2$ TMDs, plays mostly an indirect role and that hybridization between different $d$ orbitals is the dominant feature. We investigate trends across the periodic table and interpret the variations of the calculated crystal and ligand fields in terms of the change of charge-transfer energy, which allows developing simple chemical intuition.
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