We theoretically investigate the electronic states in monolayer $\mathrm{Nb}{\mathrm{Se}}_2$ and develop continuous models to describe these states in Fermi pockets. In $1H$-type metallic transition metal dichalcogenides (TMDCs), the Fermi surface consists of three pockets enclosing the $\mathrm{\Gamma },$ $K,$ and $K^{\prime }$ points. We reveal that the conventional effective model used for semiconducting TMDCs is not sufficient to describe the electronic states in metallic TMDCs and thus introduce a scheme to construct the effective model from the first-principle results. All models can be represented by a $3\times 3$ Hamiltonian and well reproduce electronic states around the Fermi energy in terms of the orbital composition and the phase factor. We also show that the $p$ orbitals in chalcogen atoms, which are ignored in the conventional $2\times 2$ model, play a crucial role in metallic TMDCs. Although the aim of these models is to reproduce electronic states, they can well describe states near the high-symmetry points and the profile of Berry curvature in wave-vector space. The continuous model can be a handleable tool to describe the electronic states and to analyze the transport phenomena in metallic TMDCs.

中文翻译：

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1H型金属过渡金属二硫化二锡单层的三轨道连续模型

我们从理论上研究单层电子态 $铌{硒}_2$并建立连续模型来描述费米口袋中的这些状态。在$\mathrm{1个}H$型金属过渡金属二卤化物（TMDC），费米表面由三个囊袋组成 $\mathrm{\Gamma }，$ $ķ，$ 和 ${ķ}^{\prime }$点。我们发现，用于半导体TMDC的常规有效模型不足以描述金属TMDC中的电子状态，因此引入了从第一原理结果构建有效模型的方案。所有模型都可以用$3\times 3$哈密​​顿量和哈密顿量根据轨道组成和相位因子在费米能量附近重现电子态。我们还表明$p$ 硫族原子中的轨道，在常规方法中被忽略 $2\times 2$模型，在金属TMDC中起着至关重要的作用。尽管这些模型的目的是重现电子状态，但它们可以很好地描述波矢量空间中高对称点附近的状态以及Berry曲率的轮廓。连续模型可以用来描述电子状态并分析金属TMDC中的传输现象。