Mariano Lorenzo A, Vlaisavljevich Bess, Poloni Roberta
Grenoble-INP, SIMaP, University of Grenoble-Alpes, CNRS, F-38042 Grenoble, France.
Department of Chemistry, University of South Dakota, Vermillion, South Dakota 57069, United States.
J Chem Theory Comput. 2020 Nov 10;16(11):6755-6762. doi: 10.1021/acs.jctc.0c00628. Epub 2020 Oct 27.
The spin-state energetics of six Fe(II) molecular complexes are computed using the linear-response Hubbard approach within DFT. The adiabatic energy differences, Δ, between the high-spin ( = 2) and the low-spin ( = 0) states are computed and compared with accurate-coupled cluster-corrected CASPT2 results. We show that DFT+U fails in correctly capturing the ground state for strong-field ligands yielding Δ that are almost constant throughout the molecular series. This bias toward high spin together with the metal/ligand charge transfer upon correction are here quantified and explained using molecular orbital diagrams involving both σ- and π-bonding interactions. With increasing ligand-field strengths this bias also increases owing to the stronger molecular character of the metal/ligand Kohn-Sham orbitals thus resulting in large deviations from the reference larger than 4 eV. Smaller values of can be employed to mitigate this effect and recover the right energetics.
使用密度泛函理论（DFT）中的线性响应哈伯德方法计算了六种Fe(II)分子配合物的自旋态能量。计算了高自旋（S = 2）和低自旋（S = 0）态之间的绝热能量差Δ，并与精确耦合簇校正的CASPT2结果进行了比较。我们表明，对于强场配体，DFT+U无法正确捕捉基态，所得到的Δ在整个分子系列中几乎是恒定的。这种对高自旋的偏向以及校正时的金属/配体电荷转移，在此使用涉及σ键和π键相互作用的分子轨道图进行了量化和解释。随着配体场强度的增加，这种偏向也会增加，这是由于金属/配体科恩-沙姆轨道的分子特征更强，从而导致与参考值的偏差大于4 eV。可以采用较小的U值来减轻这种影响并恢复正确的能量学。
