Magnetic exchange interactions in binuclear and tetranuclear iron(III) complexes described by spin-flip DFT and Heisenberg effective Hamiltonians,Journal of Computational Chemistry

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Magnetic exchange interactions in binuclear and tetranuclear iron(III) complexes described by spin-flip DFT and Heisenberg effective Hamiltonians
Journal of Computational Chemistry ( IF 3.4 ) Pub Date : 2022-06-14 , DOI: 10.1002/jcc.26941
Saikiran Kotaru ₁ , Sven Kähler ₁ , Maristella Alessio ₁ , Anna I Krylov ₁

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Low-energy spectra of single-molecule magnets (SMMs) are often described by Heisenberg Hamiltonians. Within this formalism, exchange interactions between magnetic centers determine the ground-state multiplicity and energy separation between the ground and excited states. In this contribution, we extract exchange coupling constants (J) for a set of iron (III) binuclear and tetranuclear complexes from all-electron calculations using non-collinear spin-flip time-dependent density functional theory (NC-SF-TDDFT). For 12 binuclear complexes with J-values ranging from −6 to −132 cm⁻¹, our benchmark calculations using the short-range hybrid ωPBEh functional and 6-31G(d,p) basis set agree well with the experimentally derived values (mean absolute error of 4.7 cm⁻¹). For the tetranuclear SMMs, the computed J constants are within 6 cm⁻¹ from the experimentally derived values. We explore the range of applicability of the Heisenberg model by analyzing bonding patterns in these Fe(III) complexes using natural orbitals (NO), their occupations, and the number of effectively unpaired electrons. The results illustrate the efficiency of the spin-flip protocol for computing the exchange couplings and the utility of the NO analysis in assessing the validity of effective spin Hamiltonians.

中文翻译：

双核和四核铁 (III) 配合物中的磁交换相互作用由自旋翻转 DFT 和海森堡有效哈密顿量描述

Heisenberg Hamiltonians 通常描述单分子磁体 (SMM) 的低能谱。在这种形式主义中，磁中心之间的交换相互作用决定了基态的多重性和基态与激发态之间的能量分离。在此贡献中，我们使用非共线自旋翻转时间相关密度泛函理论 (NC-SF-TDDFT) 从全电子计算中提取一组铁 (III) 双核和四核配合物的交换耦合常数 ( J ) 。对于J值范围为 −6 至 −132 cm ⁻¹的 12 个双核复合物，我们的基准计算使用短程混合ωPBEh 泛函和 6-31G(d,p) 基组与实验得出的值非常吻合（平均绝对误差为 4.7 cm ^-1）。对于四核 SMM，计算出的J常数与实验得出的值相差 6 cm ^-1以内。我们通过使用自然轨道 (NO)、它们的占据和有效未配对电子的数量分析这些 Fe(III) 配合物中的键合模式来探索海森堡模型的适用范围。结果说明了自旋翻转协议计算交换耦合的效率和 NO 分析在评估有效自旋哈密顿量有效性方面的效用。

更新日期：2022-06-14

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