BeSiN_2和MgSiN_2晶体稳定性和电子结构的第一性原理研究

First Principle Studies on the Stability and Electronic Structures of BeSiN_2 and MgSiN_2

自然条件下,BeSiN_2和MgSiN_2以正交晶系(α相)存在.施加压力之后,这两种材料会产生新的相(分别记作β相,γ相和δ相).运用密度泛函理论对材料的晶格参数进行了模拟;使用线性响应函数方法(密度泛函微扰理论)计算了材料的声子色散关系,得出:在无外界压力时,γ-BeSiN_2,δ-BeSiN_2和γ-MgSiN_2结构不稳定,而其余各相可以稳定存在.运用密度泛函理论(分别使用PBE泛函和HSE泛函)得到其能带结构:其中β-BeSiN_2和β-MgSiN_2具有直接带隙,而其他6种相都是间接带隙;之后运用多体微扰理论框架下的GW方法对BeSiN_2和MgSiN_2布里渊区高对称点的能量值进行了修正;其中α-MgSiN_2的带隙宽度为5.55 e V,和实验值5.6 e V吻合.

BeSiN2 and MgSiN2 own potential applications in luminescence. Naturally,they exist in orthorhombic crystals（ α phase）. Under external pressure,both of them transform into new phases（ β,γ and δ phase）. Lattice parameters of BeSiN2 and MgSiN2 polymorphs are calculated by employing density functional theory. Phonon dispersions are obtained by linear response functions（ density functional perturbation theory）. γ-BeSiN2,δ-BeSiN2andγ-MgSiN2 are dynamically unstable,while all the other phases are stable at ambient pressure. Band structures are calculated by employing both PBE and HSE functional,results indicate that only β-BeSiN2 and β-MgSiN2 have direct band gaps among 8 phases. Band energies at high symmetry points in Brillouin zone are corrected by many-body perturbation theory. α-MgSiN2 has an indirect band gap of 5. 55 e V,which is close to experimental result 5. 6 e V.