Using first‐principles lattice dynamics calculations, new phase transitions driven by soft phonon modes in CsPbBr₃, from the high‐symmetry cubic structure $Pm3m$ to hypothetical structures, are predicted. The structural, electronic, and dielectric properties of the new phases are determined. A ferroelectric phase with $Pmc{2}_1$ symmetry is found to be more stable than the experimentally observed phases. It is suggested that it is a good candidate as a ground state. It is demonstrated that the out‐of‐phase rotations of the ${\text{PbBr}}_6$ octahedra determine a more stable crystal lattice than the in‐phase rotations. All predicted structures show semiconductor character, with bandgap values between 1.44 and 1.87 eV. The bandgap increases with increasing PbBr bond length and the angle of rotation of the ${\text{PbBr}}_6$ octahedron. The dielectric tensor, Born effective charges, and spontaneous polarization are also calculated. The optical dielectric constant shows low sensitivity to unit cell volume and symmetry of the structures. The Born effective charges are sensitive to lattice symmetry, as they are related to the directions of charge transfer between ions, whereas the cell volume has no significant effect on their values. The infrared and Raman vibration modes of the three structures are also determined.

中文翻译：

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CsPbBr3的软声子模式驱动的新相变：密度泛函理论研究

使用第一性原理晶格动力学计算，由高对称立方结构在CsPbBr _3中由软声子模式驱动的新相变$P米3米$假设结构。确定了新相的结构，电子和介电性能。铁电相$P米C{2}_{\mathrm{1个}}$发现对称性比实验观察到的相更稳定。建议将其作为基态的良好候选者。证明了齿轮的异相旋转${\text{铅溴}}_6$八面体确定了比同相旋转更稳定的晶格。所有预测的结构均显示半导体特性，带隙值介于1.44和1.87 eV之间。带隙随PbBr键长和键的旋转角度的增加而增加。${\text{铅溴}}_6$八面体。还计算了介电张量，Born有效电荷和自发极化。光学介电常数显示出对晶胞体积和结构对称性的低敏感性。玻恩有效电荷对晶格对称性敏感，因为它们与离子之间的电荷转移方向有关，而晶胞体积对其值无明显影响。还确定了这三种结构的红外和拉曼振动模式。