BeSiN_2和MgSiN_2晶体稳定性和电子结构的第一性原理研究

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.

First Principle Studies on the Stability and Electronic Structures of BeSiN2 and MgSiN2

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,γand 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-BeSiN2 and γ-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.a-MgSiN2 has an indirect band gap of 5.55 eV,which is close to experimental result 5.6 eV.