Zvejnieks Guntars, Mastrikov Yuri, Gryaznov Denis
Institute of Solid State Physics, University of Latvia, Kengaraga Str. 8, Riga, 1063, Latvia.
Sci Rep. 2023 Sep 30;13(1):16446. doi: 10.1038/s41598-023-43381-7.
We present theoretical justification for distorted Ruddlesden-Popper (RP) phases of the first-order by using hybrid density functional theory (DFT) calculations and group-theoretical analysis. We, thus, demonstrate the existence of the Jahn-Teller effect around an Fe[Formula: see text] ion in Sr[Formula: see text]FeO[Formula: see text]. On the calculation side, we have established a combination of Wu-Cohen (WC) exchange and Perdew-Wang (PW) correlation in a three-parameter functional WC3PW, giving the most accurate description of Sr[Formula: see text]FeO[Formula: see text] from the comparison of three hybrid DFT functionals. Self-consistently obtained Hartree-Fock exact exchange of 0.16 demonstrates consistent results with the experimental literature data. Importantly, we explain conditions for co-existing proper and pseudo-Jahn-Teller effects from the crystalline orbitals, symmetry-mode analysis and irreps products. Moreover, phonon frequency calculations support and confirm the results of symmetry-mode analysis. In particular, the symmetry-mode analysis identifies a dominating irreducible representation of the Jahn-Teller mode (X2+) and corresponding space group (SG) of ground state structure (SG Cmce model). Therefore, the usually suggested high-symmetry tetragonal crystal structure (SG I4/mmm model) is higher in energy by 121 meV/f.u. (equivalent to the Jahn-Teller stabilization energy) compared with the distorted low-symmetry structure (SG Cmce model). We also present diffraction patterns for the two crystal symmetries to discuss the differences. Therefore, our results shed light on the existence of low-symmetry RP phases and make possible direct comparisons with future experiments.
我们通过使用杂化密度泛函理论（DFT）计算和群论分析，给出了一阶扭曲的Ruddlesden-Popper（RP）相的理论依据。因此，我们证明了在Sr₂FeO₄中Fe²⁺离子周围存在Jahn-Teller效应。在计算方面，我们在三参数泛函WC3PW中建立了Wu-Cohen（WC）交换和Perdew-Wang（PW）关联的组合，通过对三种杂化DFT泛函的比较，给出了对Sr₂FeO₄最准确的描述。自洽得到的0.16的Hartree-Fock精确交换与实验文献数据显示出一致的结果。重要的是，我们从晶体轨道、对称模式分析和不可约表示乘积解释了共存的正常和伪Jahn-Teller效应的条件。此外，声子频率计算支持并证实了对称模式分析的结果。特别是，对称模式分析确定了Jahn-Teller模式（X2+）的主导不可约表示以及基态结构的相应空间群（SG Cmce模型）。因此，通常建议的高对称四方晶体结构（SG I4/mmm模型）与扭曲的低对称结构（SG Cmce模型）相比，能量高121 meV/f.u.（相当于Jahn-Teller稳定能）。我们还给出了两种晶体对称性的衍射图案以讨论差异。因此，我们的结果揭示了低对称RP相的存在，并使得与未来实验进行直接比较成为可能。
