TiN多型体高压相变的第一性原理计算

Ab initio calculation of pressure-induced phase transition of TiN polytypes

基于密度泛函理论框架下的赝势平面波方法,计算了B1(氯化钠结构)、B2(氯化铯结构)、B3(闪锌矿结构)、Bk(六方氮化硼结构)、Bh(碳化钨结构)和B81(砷化镍结构)6种TiN多型体的晶体结构、体积弹性模量和相对稳定性.计算指出,不存在B4(纤锌矿)结构的TiN.通过不同外压下的晶格弛豫得到每种结构的焓,发现外压低于345GPa时TiN最稳定的结构是B1结构,在345GPa以上B2结构的TiN最稳定.TiN从B1结构到B2结构的相变伴随着体积和弹性模量的变化.

Based on a plane wave pseudopotential method within the framework of density functional theory,equilibrium structure,bulk modulus,and relative stability were calculated for 6 kinds of TiN polytypes including B1（NaCl structure）,B2（CsCl structure）,B3（zincblende structure）,Bk（hexagonal BN structure）,Bh（WC structure） and B81（NiAs structure）.Theoretical calculation also showed that TiN can not exist in B4（wurtizite） structure.Through geometry optimization under hydrostatic pressure,the enthalpy of each TiN phase at different pressures was obtained.It was found that TiN with B1 structure is the most stable phase at pressure lower than about 345 GPa,whereas B2 TiN is the most stable at pressure above 345 GPa.Volume discontinuity and bulk modulus change can be observed during the transition from B1 to B2 phase.