Two-Dimensional Ionic Crystals: The Cases of IA-VII Alkali Halides and IA-IB CsAu
Two-Dimensional Ionic Crystals: The Cases of IA-VII Alkali Halides and IA-IB CsAu
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DOI：
10.7566/jpsj.91.094606
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发表时间：
2022-03
影响因子：
1.7
通讯作者：
S. Ono
中科院分区：
文献类型：
--
作者：
S. Ono
被称为离子晶体的碱金属卤化物具有NaCl型或CsCl型结构作为基态。我们从第一性原理研究二维（2D）离子晶体的结构，振动和电子性质。两种潜在的结构是六方和四面体作为结构模板进行了研究。通过声子色散计算，在20个碱金属卤化物的六方和四方结构中，分别有8个和16个是动态稳定的。电子能隙的范围从6.8 eV的LiF到3.9 eV的RbI和CsI的tetraorthane结构内的广义梯度近似。通过考虑Madelung能和核-核排斥，我们提出了一个硬球模型，该模型可以解释最近邻键长和二维碱金属卤化物的结合能。在四元结构中的2D CsAu也被预测为作为仅包括金属元素的离子晶体是稳定的，显示出比3D对应物高的2.6 eV的带隙。
The alkali halides, known as ionic crystals, have the NaCl-type or CsCl-type structure as the ground state. We study the structural, vibrational, and electronic properties of two-dimensional (2D) ionic crystals from first-principles. Two potential structures that are hexagonal and tetragonal are investigated as structural templates. Through phonon dispersion calculations, 8 and 16 out of 20 alkali halides in the hexagonal and tetragonal structures are dynamically stable, respectively. The electron energy gaps range from 6.8 eV for LiF to 3.9 eV for RbI and CsI in the tetragonal structure within the generalized gradient approximation. By considering the Madelung energy and the core-core repulsion, we propose a hard sphere model that accounts for the nearest-neighbor bond length and the cohesive energy of 2D alkali halides. The 2D CsAu in the tetragonal structure is also predicted to be stable as an ionic crystal including only metallic elements, showing a band gap of 2.6 eV that is higher than that of the 3D counterparts.