Ab Initio Crystal Field for Lanthanides
Ab Initio Crystal Field for Lanthanides
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DOI：
10.1002/chem.201605102
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发表时间：
2017-03-01
影响因子：
4.3
通讯作者：
Chibotaru, Liviu F.
中科院分区：
文献类型：
--
作者：
Ungur, Liviu;Chibotaru, Liviu F.
本文描述了一种第一性原理推导稀土元素晶场参数的从头算方法。将该方法应用于[Tb(Pc)(2)](-)(Pc=酞菁)和Dy4K2([(DyKO)-K-4-O-2(OtBu)(12)])配合物的Cf参数分析，并与常用的近似描述和模型描述进行了比较。结果发现，几何对称化的应用，以及静电点电荷和唯象CF模型的使用，导致实验几何中基于从头计算的预测产生了不可接受的巨大偏差。结果表明，通过引入动态电子关联效应(CASPT2步)和加入5d壳层的电子组态，标准CASSCF(完全活动空间自洽场)计算(4f轨道在活动空间)的预测可以被系统地改进。这以研究得很好的Er-trensal复合体(H(3)trensal=2，2，2-tris(salicylideneimido)trimethylamine).为例根据配体中的真实电荷分布计算，该络合物中的静电对CF参数的贡献不到总CF分裂的一半，因此表明共价效应起主导作用。这一分析表明，从头算晶场是描述稀土元素的必要工具。
An ab initio methodology for the first-principle derivation of crystal-field (CF) parameters for lanthanides is described. The methodology is applied to the analysis of CF parameters in [Tb(Pc)(2)](-)(Pc=phthalocyanine) and Dy4K2 ([(DyKO)-K-4-O-2(OtBu)(12)]) complexes, and compared with often used approximate and model descriptions. It is found that the application of geometry symmetrization, and the use of electrostatic point-charge and phenomenological CF models, lead to unacceptably large deviations from predictions based on ab initio calculations for experimental geometry. It is shown how the predictions of standard CASSCF (Complete Active Space Self-Consistent Field) calculations (with 4f orbitals in the active space) can be systematically improved by including effects of dynamical electronic correlation (CASPT2 step) and by admixing electronic configurations of the 5d shell. This is exemplified for the well-studied Er-trensal complex (H(3)trensal=2,2,2-tris(salicylideneimido)trimethylamine). The electrostatic contributions to CF parameters in this complex, calculated with true charge distributions in the ligands, yield less than half of the total CF splitting, thus pointing to the dominant role of covalent effects. This analysis allows the conclusion that ab initio crystal field is an essential tool for the decent description of lanthanides.