硅石墨烯g-SiC_(7)的Si分布和结构的第一性原理研究

First principles study of distributions of Si atoms and structures of siligraphene g-SiC_(7)

硅石墨烯(siligraphene)作为石墨烯和硅烯的复合物,由于其具有石墨烯和硅烯不具备的许多优异性能而受到了广泛关注.Siligraphene的性质与Si原子的分布以及它的结构密切相关,但是目前对siligraphene的研究主要限于Si的规则分布和具有高对称性的平面结构.为了超越这些限制,本文基于密度泛函理论研究了siligraphene g-SiC_(7)所有可能的Si分布及其平面和非平面结构.首先从g-SiC_(7)的35960种Si分布中筛选出了365种不等价的Si分布,然后针对每个不等价的Si分布,比较了平面结构和非平面结构的稳定性.就Si分布而言,Si原子倾向于聚集在一起以降低能量,而更分散的Si分布通常具有更高的能量;就结构的平面性而言,研究发现存在很多的非平面结构,其能量明显低于平面结构.在所有可能的Si分布中,仅有8个平面结构对面外扰动是稳定的.本文进一步研究了能量最低三种结构的动力学、热力学和机械稳定性,发现它们都是稳定的.能带计算发现,尽管能量最低的几种结构存在明显的翘曲,它们在第一布里渊区中两个狄拉克能谷仍得以保留,并且在狄拉克点处打开了相当大的带隙.本文计算了其贝里曲率,发现在不等价狄拉克能谷处的贝里曲率是相反的,这表明系统具有能谷自由度.研究表明,siligraphene倾向于具有更集中的Si分布和翘曲结构,并且最稳定的结构具有良好的电子性质.

Siligraphene,as a composite of graphene and silicene,has attracted widespread attraction since it has many excellent properties that neither of graphene and silicene possesses.The properties of siligraphene are closely related to the distribution of Si atoms and its structure,but most of the current researches of siligraphene focus on the regular distribution of Si atoms and the planar structure with high symmetry.Therefore,we study in this work all possible Si atoms’distributions with planar and nonplanar structures for siligraphene g-SiC_(7)based on density functional theory.At first,365 kinds of inequivalent Si atoms’distributions in g-SiC_(7)are selected out from the 35960 kinds of Si atoms’distributions,and then for each inequivalent Si atoms’distribution,a comparison of the stability between the planer and nonplanar structures is made.In terms of the Si distribution,the Si atoms tend to gather together to lower the energy.The more dispersed Si atoms’distribution usually has appreciably higher energy.In terms of the planarity of the structures,it is found that there are many non-planar structures with significantly lower energy than the planar ones.For all possible Si atoms’distributions,there are only 8 planar structures which are stable against out-of-plane perturbations.We further study the dynamic,thermodynamic and mechanical stability of the structures with the lowest energies and find that they are stable.The energy band calculation shows that two Dirac valleys still persist in the first Brillouin zone despite their appreciable structure deformation,and a considerable band gap is opened at the Dirac point.We calculate the Berry curvatures and find that the Berry curvatures at the inequivalent valleys are opposite,indicating that the system has valley degree of freedom.Our research shows that siligraphene is more likely to have a buckled structure and a more concentrated silicon atoms’distribution,and the most stable structures have good electronic properties.