Fast and reliable ab initio calculation of crystal field splittings in lanthanide complexes

P P Hallmen; C Köppl; G Rauhut; H Stoll; J van Slageren

doi:10.1063/1.4998815

Fast and reliable ab initio calculation of crystal field splittings in lanthanide complexes

J Chem Phys. 2017 Oct 28;147(16):164101. doi: 10.1063/1.4998815.

Authors

P P Hallmen¹, C Köppl², G Rauhut², H Stoll², J van Slageren¹

Affiliations

¹ Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
² Institute of Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.

PMID: 29096514
DOI: 10.1063/1.4998815

Abstract

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]^-.