Verma Pragya, Varga Zoltan, Klein Johannes E M N, Cramer Christopher J, Que Lawrence, Truhlar Donald G
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455-0431, USA.
Phys Chem Chem Phys. 2017 May 24;19(20):13049-13069. doi: 10.1039/c7cp01263b.
Our ability to understand and simulate the reactions catalyzed by iron depends strongly on our ability to predict the relative energetics of spin states. In this work, we studied the electronic structures of Fe ion, gaseous FeO and 14 iron complexes using Kohn-Sham density functional theory with particular focus on determining the ground spin state of these species as well as the magnitudes of relevant spin-state energy splittings. The 14 iron complexes investigated in this work have hexacoordinate geometries of which seven are Fe(ii), five are Fe(iii) and two are Fe(iv) complexes. These are calculated using 20 exchange-correlation functionals. In particular, we use a local spin density approximation (LSDA) - GVWN5, four generalized gradient approximations (GGAs) - BLYP, PBE, OPBE and OLYP, two non-separable gradient approximations (NGAs) - GAM and N12, two meta-GGAs - M06-L and M11-L, a meta-NGA - MN15-L, five hybrid GGAs - B3LYP, B3LYP*, PBE0, B97-3 and SOGGA11-X, four hybrid meta-GGAs - M06, PW6B95, MPW1B95 and M08-SO and a hybrid meta-NGA - MN15. The density functional results are compared to reference data, which include experimental results as well as the results of diffusion Monte Carlo (DMC) calculations and ligand field theory estimates from the literature. For the Fe ion, all functionals except M11-L correctly predict the ground spin state to be quintet. However, quantitatively, most of the functionals are not close to the experimentally determined spin-state splitting energies. For FeO all functionals predict quintet to be the ground spin state. For the 14 iron complexes, the hybrid functionals B3LYP, MPW1B95 and MN15 correctly predict the ground spin state of 13 out of 14 complexes and PW6B95 gets all the 14 complexes right. The local functionals, OPBE, OLYP and M06-L, predict the correct ground spin state for 12 out of 14 complexes. Two of the tested functionals are not recommended to be used for this type of study, in particular M08-SO and M11-L, because M08-SO systematically overstabilizes the high spin state, and M11-L systematically overstabilizes the low spin state.
我们理解和模拟铁催化反应的能力在很大程度上取决于我们预测自旋态相对能量的能力。在这项工作中，我们使用Kohn-Sham密度泛函理论研究了铁离子、气态FeO和14种铁配合物的电子结构，特别关注确定这些物种的基态自旋态以及相关自旋态能量分裂的大小。这项工作中研究的14种铁配合物具有六配位几何结构，其中七种是Fe(ii)配合物，五种是Fe(iii)配合物，两种是Fe(iv)配合物。这些是使用20种交换相关泛函计算的。具体来说，我们使用了局部自旋密度近似(LSDA)-GVWN5、四种广义梯度近似(GGAs)-BLYP、PBE、OPBE和OLYP、两种不可分离梯度近似(NGAs)-GAM和N12、两种meta-GGAs-M06-L和M11-L、一种meta-NGA-MN15-L、五种杂化GGAs-B3LYP、B3LYP*、PBE0、B97-3和SOGGA11-X、四种杂化meta-GGAs-M06、PW6B95、MPW1B95和M08-SO以及一种杂化meta-NGA-MN15。将密度泛函理论的结果与参考数据进行了比较，参考数据包括实验结果以及扩散蒙特卡罗(DMC)计算结果和文献中的配体场理论估计值。对于铁离子，除M11-L外的所有泛函都正确地预测基态自旋态为五重态。然而，从定量角度来看，大多数泛函与实验测定的自旋态分裂能量并不接近。对于FeO，所有泛函都预测五重态是基态自旋态。对于14种铁配合物，杂化泛函B3LYP、MPW1B95和MN15正确地预测了14种配合物中13种的基态自旋态，而PW6B95则正确预测了所有14种配合物的基态自旋态。局部泛函OPBE、OLYP和M06-L预测了14种配合物中12种的正确基态自旋态。不建议将两种测试泛函，特别是M08-SO和M11-L用于此类研究，因为M08-SO系统性地过度稳定了高自旋态，而M11-L系统性地过度稳定了低自旋态。
