高压下MgN8晶体结构理论模拟与物性研究

基于密度泛函理论第一性原理的方法,使用CALYPSO结构搜索技术结合VASP软件,在0~100 GPa压强范围内对MgN8的晶体结构进行预测,并对预测的结构进行系统研究。结果表明:在常压下,空间群为P4/mbm的α-MgN8晶体结构的焓值最低;当压强达到24.3 GPa和68.3 GPa时发生相变,分别相变成空间群为P4/mnc的β-MgN8相和空间群为Cmcm的γ-MgN8相,两次相变均为对应体积坍塌的一级相变。电子性质计算结果表明,α-MgN8相的导带与价带之间具有3.09 eV的带隙,表明该结构具有非金属性;β相和γ相具有明显的金属特征。Bader电荷转移计算表明,随着压力的增加,Mg原子向N原子转移的电荷逐渐增多。

Theoretical Simulation and Physical Properties of MgN8 Crystal Structure under High Pressure

Based on the first principle of density functional theory,the crystal structure of MgN8 was predicted in the pressure range of 0–100 GPa by using CALYPSO structure search technique and VASP software.After systematically studying the predicted structure,it was found that the enthalpy of α-MgN8 crystal with space group P4/mbm was the lowest at ambient pressure.The phase was changed to β-MgN8 phase of P4/mnc andγ-MgN8 phase of Cmcm when the pressure reached 24.3 GPa and 68.3 GPa,respectively.And both of the phase transitions were the first order phase transition of corresponding volume collapse.The calculated results of electronic properties suggested that the existence of a band gap of 3.09 eV between the conduction band and valence band ofα-MgN8 phase revealed the non-gold properties of the structure,whereas the obvious metal characteristics appeared in the β-MgN8 phase and γ-MgN8 phase.Bader charge transfer calculation showed that the charge which transferred from Mg atom to N atom,increased gradually with the increase of pressure.