Pascale Fabien, Mustapha Sami, D'Arco Philippe, Dovesi Roberto
Laboratoire de Physique et Chimie Théoriques, Université de Lorraine, CNRS, UMR 7019, F-54506 Vandoeuvre-lès-Nancy, France.
Institut de Mathématiques de Jussieu, Sorbonne Université, UMR 7586, F-75005 Paris, France.
Materials (Basel). 2023 Feb 12;16(4):1532. doi: 10.3390/ma16041532.
The occupancy of the d shell in KFeF3 is t2g4eg2, with five α and one β electrons. The Jahn-Teller lift of degeneracy in the t2g sub-shell produces a tetragonal relaxation of the unit cell (4.09 vs. 4.22 Å, B3LYP result) not observed experimentally. In order to understand the origin of this apparent contradiction, we explored, with a 2 × 2 × 2 supercell (40 atoms per cell), all possible local structures in which contiguous Fe atoms have a different occupancy of the t2g orbitals with the minority spin electron. A total of 6561 configurations (with occupancies from (8,0,0) to (3,2,2) of the 3 t2g orbitals of the 8 Fe atoms) have been explored, with energies in many cases lower (by up to 1550 μEh per 2 Fe atoms) than the one of the fully ordered case, both for the ferromagnetic and the anti-ferromagnetic solutions. The results confirm that the orientation of the β d electron of Fe influences the electrostatics (more efficient relative orientation of the Fe quadrupoles of the d shell) of the system, but not the magnetic interactions. Three hybrid functionals, B3LYP, PBE0, and HSE06, provide very similar results.
在KFeF₃中，d壳层的占据情况为t₂g⁴eg²，有五个α电子和一个β电子。t₂g子壳层中简并的 Jahn-Teller 效应导致晶胞发生四方弛豫（4.09 Å 对 4.22 Å，B3LYP 结果），但实验中未观察到。为了理解这一明显矛盾的起源，我们使用一个 2×2×2 超胞（每个晶胞 40 个原子）探索了所有可能的局部结构，其中相邻的 Fe 原子对具有少数自旋电子的 t₂g 轨道有不同的占据情况。总共探索了 6561 种构型（8 个 Fe 原子的 3 个 t₂g 轨道的占据情况从(8,0,0)到(3,2,2)），对于铁磁和反铁磁解，在许多情况下其能量都比完全有序情况的能量低（每 2 个 Fe 原子低达 1550 μEh）。结果证实，Fe 的β d 电子的取向影响系统的静电作用（d 壳层的 Fe 四极矩的相对取向更有效），但不影响磁相互作用。三种杂化泛函 B3LYP、PBE0 和 HSE06 给出了非常相似的结果。
