【摘要】 通过运用基于密度泛函理论的第一性原理计算方法结合广义梯度近似对压力下CaN₂的结构稳定性和电子结构进行了理论研究.对结构稳定性的研究表明,ZnCl₂型结构是CaN₂在环境压力下最稳定的结构,而实验上观察到的CaC₂-I型结构是CaN₂高压下（>8.7 GPa）的稳定性结构.在50 GPa的压力范围内,CaN₂将发生从ZnCl₂型结构到ThC₂型结构再到CaC₂-I型结构的两次压致结构相变,其相变压力分别为0.81 GPa和8.77 GPa.而对电子结构的研究表明ZnCl₂型、ThC₂型和CaC₂-I型三种结构的CaN₂都表现出了金属特征,三种结构CaN₂当中Ca-N键的离子-共价性特征和N原子间的N=N双键特征得到了确认.更多还原

【Abstract】 The structural stabilities and electronic properties of CaN₂ under pressure have been investigated by using first-principles plane-wave pseudopotential density functional theory within the generalized gradient approximation（ GGA）. The obtained results show that the ZnCl₂-type structure is the ground-state of CaN₂ at ambient pressure. The CaC₂-I-type structure observed in experiment,however,becomes the thermodynamically preferred phase at high pressures（ > 8. 77 GPa）. Two pressure-induced phase transitions are found at0. 81 and 8. 77 GPa,from the initial ZnCl₂-type structure（ Space group Pna21） through a ThC₂-type structure（ Space group C2 / c） to a CaC₂-I-type structure（ Space group I4 / mmm）. Moreover,electronic structure calculations reveal that CaN₂ in all three structures are metallic. The covalent-ionic nature of Ca-N bonding and the covalent N = N double bonding in all three CaN₂ structures are confirmed.更多还原