碱土金属X（X=Be，Mg，Ca和Sr）掺杂二维SnS2材料的第一性原理研究

基于密度泛函理论的第一性原理研究赝势平面波方法，计算了碱土金属X(X=Be, Mg, Ca和Sr)掺杂二维单层SnS₂的电子结构、磁学性质和光学性质.结果表明：S-rich条件下的体系相较于Sn-rich更稳定，能带结构表明：在Be掺杂后，SnS₂体系从自旋向上通道和自旋向下通道完全对称的非磁性半导体转变为具有1.999μ_B磁矩的磁性半导体.在Mg掺杂后，体系转变为非磁性P型半导体；Ca和Sr两种掺杂体系由于极化程度的不同，导致在下自旋通道的能带穿过费米能级，而在上自旋通道的能带并未穿过费米能级，呈现出磁矩分别为1.973、2.000μ_B的半金属特性.同时发现X(X=Be, Mg, Ca和Sr)掺杂后，掺杂体系实部静态介电常数大幅度增加，掺杂后的SnS₂体系的极化能力增强，虚部数值在低能区明显变大，更适用于长波长光电器. Be, Mg, Ca和Sr掺杂不仅导致吸收边红移，而且提高了红外光区域的有效利用率.

First-principles study of alkaline earth metal X (X=Be, Mg, Ca and Sr) doped two-dimensional SnS2 materials

Based on the first-principles study of pseudopotential plane wave method, the electronic structures, magnetic properties and optical properties of alkaline earth metal X (X=Be, Mg, Ca and Sr) doped two-dimensional (2D) SnS2 monolayers were calculated. The results show that the systems under S-rich condition are more stable than Sn-rich, and the Ca and Sr doped systems have the smallest formation energy under S-rich condition, which are -2.674 eV and -2.422 eV, respectively. The band structures show that after Be doping, the impurity levels appear in the spin-down channel near the Fermi level, which lead to the transition of the SnS2 system from a completely symmetric non-magnetic semiconductor to a magnetic semiconductor with a magnetic moment of 1.999 μB. After Mg doping, the system transforms into a non-magnetic P-type semiconductor. Due to the different polarization degrees of Ca and Sr doped systems, the band structure of the spin-down channel passes through the Fermi level, however, the energy band of the spin-up channel does not pass through the Fermi level, showing semi-metallic properties with magnetic moments of 1.973 and 2.000 μB, respectively. At the same time, it is found that X doped systems exhibit excellent optical properties. The real part of dielectric function is greatly increased, and the polarization ability is enhanced. The value of the imaginary part becomes significantly larger in the low-energy region, which is more suitable for long-wavelength optoelectronic devices. Be, Mg, Ca, and Sr doped systems not only lead to a red-shift of the absorption edge, but also improve the effective utilization in the infrared region.