Evolution of Crystal Structures and Electronic Properties for Ir2P under High Pressure
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摘要: 在压强为0～100 GPa范围内，运用CALYPSO结构搜索技术，结合基于密度泛函理论中的第一性原理方法，对Ir2P晶体进行结构预测，并对预测出的晶体结构和物理性质进行细致的研究。在常压下，预测得出α-Ir2P相具有立方结构，其空间群为Fm3m，与实验所得结构一致；压强为86.4 GPa时，发生结构相变，由α-Ir2P相转变为β-Ir2P相，为四方结构，其空间群为I4/mmm。在相变过程中，晶体体积发生坍塌，并且出现不连续变化的一级相变。电子性质计算表明，86.4 GPa时，预测的β-Ir2P相中导带和价带在费米面附近发生交叠，表明其结构具有金属性质；电子局域函数计算表明，β-Ir2P相具有丰富的化学键，包括极性共价键、金属键和离子键；Bader电荷转移计算得出，由于Ir原子具有较强的电负性，β-Ir2P相中每个P原子向每个Ir原子电荷转移0.19e。Abstract: The crystals of Ir2P were predicted under the pressure ranging from 0 to 100 GPa using the CALYPSO structure exploration technique with the first-principles method based on the density functional theory. The predicted physical properties and crystal structures were examined in detail. At ambient pressure, the predicted α-Ir2P phase was found to have a cubic structure with Fm3m space group, which is consistent with the experimental structure. The pressure-induced structural transformations were unraveled, from the α-Ir2P phase to the β-Ir2P phase at 86.4 GPa. The predicted β-Ir2P phase has I4/mmm space group. In the process of phase transition, the volume of the crystal collapses and a discontinuous first order phase transition occurred. The calculation of the electronic properties showed that the predicted conduction bands and the valence bands of the β-Ir2P phase overlap near the Fermi surface at 86.4 GPa, indicating that the structure of the β-Ir2P phase has metallic properties. The electron localization function revealed that the β-Ir2P phase has a polar covalent bond, a metallic bond and an ionic bond. The Bader charge transfer calculations showed that each P atom transfers 0.19e to Ir atom, mainly due to the strong electronegativity of the Ir atoms.
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Key words:
- high pressure /
- first-principles /
- crystal structure prediction /
- Ir2P
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图 1 Ir2P的焓差曲线以及α-Ir2P相和β-Ir2P相体积随压强变化曲线
Figure 1. Calculated enthalpies per formula unit (f.u.) of pressure with respect to α-Ir2P and the calculated pressure versus volume phase diagram of α-Ir2P and β-Ir2P
图 3 86.4 GPa时β-Ir2P相的声子谱和声子态密度
Figure 3. Phonon-dispersion curves and the PHDOS of β-Ir2P at 86.4 GPa
图 4 86.4 GPa下β-Ir2P相的能带结构和电子态密度
Figure 4. Band structure and partial DOS of β-Ir2P phase at 86.4 GPa
图 5 86.4 GPa下β-Ir2P相的电子局域函数
Figure 5. Electron localization function of β-Ir2P phase at 86.4 GPa
表 1 α-Ir2P相和β-Ir2P相的平衡态晶格常数和原子位置
Table 1. Lattice parameters and atomic coordinate of α-Ir2P and β-Ir2P
Phase Pressure/GPa Space group Lattice parameters Wyckoff position Atoms Site α-Ir2P 0 Fm3m a=5.622 Å（5.535 Å*）, b=c=5.622 Å Ir1 8c(0.250, 0.250, 0.250) α=β=γ=90.0° P1 4a(0, 0, 0) β-Ir2P 86.4 I4/mmm a=b=2.694 Å, c=9.461 Å Ir1 4e(0.500, 0.500, 0.146) α=β=γ=90.0° P1 2a(0.500, 0.500, 0.500) Note: The asterisk represents the experimental data from Ref. [13]. 
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表 2 86.4 GPa下β-Ir2P相的Bader电荷转移
Table 2. Calculated Bader charges of β-Ir2P phase at 86.4 GPa
Space group Pressure/GPa Atom Number Charge value/e Charge transfer/e I4/mmm 86.4 GPa Ir 2 9.19 –0.19 P 1 4.62 0.38
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