Ab initio calculations of crystal field splittings and magnetic properties of lanthanide complexes are usually performed using 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). Because this approach becomes very time-consuming for large molecules, simplifications have been proposed in the literature to determine the state-averaged orbitals by configuration-averaged Hartree-Fock (CAHF) instead of CASSCF. We present an approach which is an extension of the CAHF method. We combine the techniques of local density fitting with CAHF and achieve a significant speedup compared to CASSCF without loss in accuracy. To assess the performance of our method, we apply it to three well-known molecules, namely, Er[N(SiMe₃)₂]₃, Er(trensal), and the double-decker (NBu₄)⁺ [Er(Pc)₂]⁻.

中文翻译：

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镧系元素络合物晶体场分裂的快速可靠的从头算

从头算镧系元素配合物的晶体场分裂和磁性能的计算通常使用状态平均的完整有源空间自洽场（CASSCF）计算以及随后的自旋轨道计算（结合了CASSCF波函数（CASSCF /自旋与态相互作用）进行）耦合）。由于这种方法对于大分子而言非常耗时，因此在文献中提出了简化方法，即通过配置平均的Hartree-Fock（CAHF）而不是CASSCF来确定状态平均的轨道。我们提出了一种方法，它是CAHF方法的扩展。我们将局部密度拟合技术与CAHF相结合，与CASSCF相比，可实现显着的加速，而不会降低精度。为了评估我们方法的性能，我们将其应用于三个众所周知的分子，即₃）₂ ] ₃，Er（trensal）和双层（NBu ₄）⁺ [Er（Pc）₂ ] ^-。