Pascale Fabien, D'Arco Philippe, Lacivita Valentina, Dovesi Roberto
Université de Lorraine-Nancy, CNRS, Laboratoire de Physique et Chimie Théoriques, UMR 7019, Vandoeuvre-les-Nancy, France.
Sorbonne Université, CNRS-INSU, Institut des Sciences de la Terre, ISTeP UMR 7193, F-75005 Paris, France.
J Phys Condens Matter. 2021 Nov 23;34(7). doi: 10.1088/1361-648X/ac36fe.
The ferromagnetic and antiferromagnetic wavefunctions of four KMF(M = Mn, Fe, Co and Ni) perovskites have been obtained quantum-mechanically with the CRYSTAL code, by using the Hartree-Fock (HF) Hamiltonian and three flavours of DFT (PBE, B3LYP and PBE0) and anGaussian type basis set. In the Fe and Co cases, with dand doccupation, the Jahn-Teller distortion of the cubic cell is as large as 0.12 Å. Various features of the superexchange interaction energies (SIE), namely additivity, dependence on the M-M distance, on theMFM̂angle, and on the adopted functional, are explored. The contribution to SIE by the Coulomb, exchange and kinetic energy terms is analyzed. It is shown that, when using density functionals, SIE clearly correlates with the amount of exact (Hartree-Fock) exchange in the functional. The effect of SIE on the equilibrium geometry and volume of the unit cell is discussed, and it is shown that the key quantity is the spin polarization of the (closed shell) F ions along the M-F-M path. The effect of thisis evaluated quantitatively for the first time. The superexchange coupling constant, evaluated at the HF level and through the Ising model, underestimates the experimental values by about 60%-70%. The more sophisticated Yamaguchi model (that takes into account the contamination of the FM and AFM spin states) does not reduce the discrepancy. The B3LYP hybrid functional overestimates the experiments. These last are bracketed by HF and PBE0. For PBE, the overestimation is huge. Finally, Mulliken population data, charge and spin density maps and density of states are used to illustrate the electronic structure.
利用CRYSTAL程序，通过使用Hartree-Fock（HF）哈密顿量、三种密度泛函理论（DFT）（PBE、B3LYP和PBE0）以及高斯型基组，从量子力学角度获得了四种钙钛矿型KMF（M = Mn、Fe、Co和Ni）的铁磁和反铁磁波函数。在Fe和Co的情况下，由于d和d轨道占据，立方晶胞的 Jahn-Teller 畸变高达0.12 Å。研究了超交换相互作用能（SIE）的各种特征，即可加性、对M-M距离、MFM̂角以及所采用泛函的依赖性。分析了库仑能、交换能和动能项对SIE的贡献。结果表明，在使用密度泛函时，SIE与泛函中精确（Hartree-Fock）交换的量明显相关。讨论了SIE对晶胞平衡几何结构和体积的影响，结果表明关键量是沿M-F-M路径的（闭壳层）F离子的自旋极化。首次对其影响进行了定量评估。在HF水平并通过伊辛模型评估的超交换耦合常数比实验值低约60%-70%。更复杂的山口模型（考虑了铁磁和反铁磁自旋态的混合）并没有减少这种差异。B3LYP杂化泛函高估了实验值。实验值介于HF和PBE0之间。对于PBE，高估非常大。最后，利用Mulliken布居数据、电荷和自旋密度图以及态密度来说明电子结构。
