Sugisaki Kenji, Toyota Kazuo, Sato Kazunobu, Shiomi Daisuke, Takui Takeji
Department of Chemistry and Molecular Materials Science, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
Phys Chem Chem Phys. 2017 Nov 15;19(44):30128-30138. doi: 10.1039/c7cp05533a.
Spin-orbit contributions to the zero-field splitting (ZFS) tensor (D tensor) of M(acac) complexes (M = V, Cr, Mn, Fe and Mo; acac = acetylacetonate anion) are evaluated by means of ab initio (a hybrid CASSCF/MRMP2) and DFT (Pederson-Khanna (PK) and natural orbital-based Pederson-Khanna (NOB-PK)) methods, focusing on the behaviour of DFT-based approaches to the D tensors against the valence d-electron configurations of the transition metal ions in octahedral coordination. Both the DFT-based approaches reproduce trends in the D tensors. Significantly, the differences between the theoretical and experimental D (D = D - (D + D)/2) values are smaller in NOB-PK than in PK, emphasising the usefulness of the natural orbital-based approach to the D tensor calculations of transition metal ion complexes. In the case of d and d electronic configurations, the D(NOB-PK) values are considerably underestimated in the absolute magnitude, compared with the experimental ones. The D tensor analysis based on the orbital region partitioning technique (ORPT) revealed that the D contributions attributed to excitations from the singly occupied region (SOR) to the unoccupied region (UOR) are significantly underestimated in the DFT-based approaches to all the complexes under study. In the case of d and d configurations, the (SOR → UOR) excitations contribute in a nearly isotropic manner, which causes fortuitous error cancellations in the DFT-based D values. These results indicate that more efforts to develop DFT frameworks should be directed towards the reproduction of quantitative D tensors of transition metal complexes with various electronic configurations and local symmetries around metal ions.
通过从头算（一种混合的CASSCF/MRMP2方法）和密度泛函理论（Pederson-Khanna（PK）方法以及基于自然轨道的Pederson-Khanna（NOB-PK）方法）评估了自旋轨道对M(acac)配合物（M = V、Cr、Mn、Fe和Mo；acac = 乙酰丙酮阴离子）的零场分裂（ZFS）张量（D张量）的贡献，重点关注基于密度泛函理论的D张量方法相对于八面体配位中过渡金属离子的价d电子构型的行为。两种基于密度泛函理论的方法都重现了D张量的趋势。值得注意的是，NOB-PK方法中理论值与实验值D（D = D - (D + D)/2）之间的差异比PK方法中的小，这突出了基于自然轨道的方法在过渡金属离子配合物D张量计算中的实用性。在d和d电子构型的情况下，与实验值相比，D(NOB-PK)值的绝对值被大幅低估。基于轨道区域划分技术（ORPT）的D张量分析表明，在基于密度泛函理论的所有研究配合物方法中，从单占据区域（SOR）到未占据区域（UOR）的激发对D的贡献被显著低估。在d和d构型的情况下，（SOR → UOR）激发以近乎各向同性的方式起作用，这导致基于密度泛函理论的D值中出现偶然的误差抵消。这些结果表明，应投入更多努力来开发密度泛函理论框架，以重现具有各种电子构型和金属离子周围局部对称性的过渡金属配合物的定量D张量。
