高压下BeP2 晶体结构与物性的理论研究

将密度泛函理论第一性原理的计算方法与晶体结构预测CALYPSO软件相结合,在0～100 GPa下对BeP₂的结构进行预测,研究了其在高压下的结构与物性.预测结果表明:在常压下, α -BeP₂相为立方结构,其空间群为I41/amd, 该结果与实验所得结构一致.当压强为30.1 GPa时, α -BeP₂相发生结构相变,由α -BeP₂相转变为β -BeP₂相,其结构转变为四方结构,空间群为P4₃2₁2.当压强为35.4 GPa时, β -BeP₂相发生结构相变,由β -BeP₂相转变为γ -BeP₂相,其结构转变为正交结构,空间群为Imma.在相变过程中,晶体结构体积发生坍塌,坍塌率分别为7.1%和10.9%, 属于一级相变.电子性质计算表明:在0 GPa下, α -BeP₂结构的带隙为0.457 eV; 在30.1 GPa下, β -BeP₂结构的带隙为0.957 eV, 为窄带隙半导体; 在35.4 GPa下, γ -BeP₂结构在费米面处其导带与价带发生交叠,具有金属性.

Structure and propertieso of BeP_2 under high pressure

At the pressure range from 0-100 GPa, the crystals of BeP₂ are predicted by using the CALYPSO structure exploration techniue combined with based on the first-principles of density functional theory and the structure and physical properties under high pressure are systematically studied. The prediction results show that the calculated results are all in good agreement with experimental in the literature, which indicated that the predicted α -BeP₂ phase has a tetragonal structure with I41/amd with space group at ambient pressure. When the pressure is 30.1 GPa, structural transformations are unraveled from α -BeP₂ phase to β -BeP₂ phase, the structure changes to tetragonal structure, and the space group is P43212. When the pressure is 35.4 GPa, structural transformations are unraveled from β -BeP₂ phase to γ -BeP₂ phase, the structure changes to orthogonal structure, and its space group is Imma. Due to the structure transition, the volume of the crystal structure collapsed and the collapse rates were 7.1% and 10.9%, respectively. So that the phase transition belonged to the first-order phase transition. The calculation of electronic properties shows that the band gap of α -BeP₂ structure is 0.457 eV at 0 GPa, and the band gap of β -BeP₂ phase band struture is 0.957 eV at 30.1 GPa which are all narrow band gap semiconductors. At 35.4 GPa, the γ -BeP₂ structure overlaps the valence band at the Fermi surface and is metallic.