摘要:
在第一性原理框架下,采用赝势平面波方法研究了三种Mg2Si同质异相体的晶胞结构、电子结构和弹性性质随压强的变化关系.研究发现,反萤石结构Mg2Si、反氯铅矿结构Mg2Si和Ni2In型Mg2Si分别在压强为0—7GPa,7.5—20.2GPa和21.9—40GPa范围内能够保持结构稳定.计算获得了不同压强下Mg2Si的弹性常数、体模量、剪切模量、杨氏模量、泊松比和各向异性因子,并探讨了压强对Mg2Si弹性性质的影响.接着还分析了三种同质异相体的电子密度、态密度、键长和布居数.结果表明：反萤石结构Mg2Si表现为半导体特征,反氯铅矿结构Mg2Si和Ni2In型Mg2Si都表现为金属特征;Si3p与Mg2p,3s轨道之间较强的杂化效应是Mg2Si同质异相体保持稳定的主要因素;反萤石结构Mg2Si中的Mg-Mg相互作用较强,而Ni2In型Mg2Si中的Mg-Si相互作用较强.计算结果与前人的实验数据和已有的理论研究结果一致.
Abstract:
The structural and the elastic properties of the Mg2Si polymorphs are calculated.The calculations are performed by using the plane-wave pseudo-potential method within the framework of first principles.The anti-fluorite structure,the anti-cotunnite structure and the Ni2In-type structure of Mg2Si can retain their mechanical stability in the pressure intervals 0—7 GPa,7.5—20.2 GPa and 21.9—40 GPa,separately.The relationships between pressure and the elastic moduli （elastic constant,bulk modulus,shear modulus,Young＇s modulus,Poisson ratio and anisotropy factor） are discussed.The electron density distribution,the density of states,the bond length and the Mulliken population of these polymorphs are systemically investigated.Our results show that the anti-fluorite Mg2Si is a semiconductor and the other two polymorphs are metallic materials.The interaction between Mg 2p,3s and Si 3p plays a dominant role in the stability of the Mg2Si polymorphs.The strongest interactions in the anti-fluorite Mg2Si and the Ni2In-type Mg2Si are Mg-Mg and Mg-Si interactions,respectively.Our results are concordant with the experimental data and the previous results.
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