高压下RhN2的结构相变，热力学性质及键的金属性对其硬度的影响的研究

Using first-principles calculations, the elastic constant, structural phase transition and effect of metallic bonding on the hardness of RhN2 under high pressure are investigated by means of the pseudopotential plane-waves method. Three structures are chosen to investigate for RhN2, namely, simple hexagonal P6/mmm (SH), orthorhombic Pnnm (marcasite) and simple tetragonal P4/mbm (ST). Our calculations show that the SH phase is energetically more stable than the other two phases at zero pressure. On the basis of the third-order Birch-Murnaghan equation of states, we find that phase transition pressure from SH to marcasite structure and marcasite to ST structure are 1.09 GPa and 354.57 GPa, respectively. Elastic constants, formation enthalpies, shear modulus, Young's modulus and Debye temperature of RhN2 are derived. The calculated values are generally speaking in good agreement with the previous theoretical results. Meanwhile, it is found that the pressure has an important influence on physical properties. Moreover, the effect of metallic bonding on the hardness of RhN2 is investigated. This is a quantitative investigation on the structural properties of RhN2, and it still awaits experimental confirmation.