Institute of Physical Chemistry , University of Stuttgart , Pfaffenwaldring 55 , 70569 Stuttgart , Germany.
Institute of Theoretical Chemistry , University of Stuttgart , Pfaffenwaldring 55 , 70569 Stuttgart , Germany.
J Chem Theory Comput. 2018 Aug 14;14(8):3998-4009. doi: 10.1021/acs.jctc.8b00184. Epub 2018 Jul 3.
State-averaged complete active space self-consistent field (CASSCF) calculations and a subsequent spin-orbit calculation mixing the CASSCF wave functions (CASSCF/state-interaction with spin-orbit coupling) is the conventional approach used for ab initio calculations of crystal-field splittings and magnetic properties of lanthanide complexes. However, this approach neglects dynamical correlation. Complete active space second-order perturbation theory (CASPT2) can be used to account for dynamical correlation but suffers from the well-known problems of multireference perturbation theory, e.g., intruder state problems. Variational multireference configuration interaction (MRCI) calculations do not show these problems but are usually not feasible due to the large size of real lanthanide complexes. Here, we present a quasi-local projected internally contracted MRCI approach which makes MRCI calculations of lanthanide complexes feasible and allows assessing the influence of dynamical correlation beyond second-order perturbation theory. We apply the method to two well-studied molecules, namely, [Er{N(SiMe)}] and {C(NH)}[Er(CO)]·11HO.
态平均完全活性空间自洽场（CASSCF）计算和随后的自旋轨道计算混合 CASSCF 波函数（CASSCF/态相互作用与自旋轨道耦合）是用于镧系配合物晶体场分裂和磁性质的从头算计算的常规方法。然而，这种方法忽略了动力学相关性。完全活性空间二阶微扰理论（CASPT2）可用于考虑动力学相关性，但存在多参考微扰理论的已知问题，例如闯入态问题。变分多参考组态相互作用（MRCI）计算不会出现这些问题，但由于实际镧系配合物的尺寸较大，通常不可行。在这里，我们提出了一种准局部投影内缩的 MRCI 方法，该方法使镧系配合物的 MRCI 计算成为可能，并允许评估超出二阶微扰理论的动力学相关性的影响。我们将该方法应用于两个研究充分的分子，即[Er{N（SiMe）}]和{C（NH）}[Er（CO）]·11HO。
