%0 DATA
%A Shashank Vittal, Rao
%A MATTEO, PICCARDO
%A Alessandro, Soncini
%D 2020
%T Spin-Orbit Coupling Descriptions of Magnetic Excitations in Lanthanide Complexes
%U https://chemrxiv.org/articles/Spin-Orbit_Coupling_Descriptions_of_Magnetic_Excitations_in_Lanthanide_Complexes/11858370
%R 10.26434/chemrxiv.11858370.v1
%2 https://chemrxiv.org/ndownloader/files/21734007
%K Lanthanides
%K spin-orbit coupling
%K spin-orbit mean field
%K Magnetic Excitations
%K ab initio multiconfigurational quantum chemical calculations
%K Crystal Field Energies
%K Cholesky Decomposition ApproximationsEfficient implementations
%X We present a number of computationally cost-effective approaches to calculate magnetic excitations (i.e. crystal ﬁeld energies and magnetic anisotropies in the lowest spin-orbit multiplet) in lanthanide complexes. In particular, we focus on the representation of the spin-orbit coupling term of the molecular Hamiltonian, which has been implemented within the quantum chemistry package CERES using various approximations to the Breit-Pauli Hamiltonian. The approximations include the (i) bare one-electron approximation, (ii) atomic mean ﬁeld and molecular mean ﬁeld approximations of the two-electron term, (iii) full representation of the Breit-Pauli Hamiltonian. Within the framework of the CERES implementation, the spin-orbit Hamiltonian is always fully diagonalized together with the electron repulsion Hamiltonian (CASCI-SO) on the full basis of Slater determinants arising within the 4f ligand ﬁeld space. For the ﬁrst time, we make full use of the Cholesky decomposition of two-electron spin-orbit integrals to speed up the calculation of the two-electron spin-orbit operator. We perform an extensive comparison of the different approximations on a set of lanthanide complexes varying both the lanthanide ion and the ligands. Surprisingly, while our results conﬁrm the need of at least a mean ﬁeld approach to accurately describe the spin-orbit coupling interaction within the ground Russell-Saunders term, we ﬁnd that the simple bare one-electron spin-orbit Hamiltonian performs reasonably well to describe the crystal ﬁeld split energies and _{g} tensors within the ground spin-orbit multiplet, which characterize all the magnetic excitations responsible for lanthanide-based single-molecule magnetism.