Ab initio ligand field approach to determine electronic multiplet properties

Abstract

A method is developed to calculate the ligand field (LF) parameters and the multiplet spectra of local magnetic centers with open d-and f -shells in solids in a parameter-free way. This method proceeds from density functional theory and employs Wannier projections of nonmagnetic band structures onto local d-or f -orbitals. Energies of multiplets and optical, as well as X-ray spectra are determined by exact numerical diagonalization of a local Hamiltonian describing Coulomb, LF, and spin-orbit interactions. The method is tested for several 3d-and 5f -compounds for which the LF parameters and multiplet spectra are experimentally well known. In this way, we obtain good agreement with experiment for La2NiO4, CaCuO2, Li2CuO2, ZnO:Co, and UO2.

Frustration enhanced by Kitaev exchange in a $\boldsymbol{\tilde{j}_{\text{eff}}=\frac12}$ triangular antiferromagnet

“…In the WF basis, the Hamiltonian is a sum of local and nonlocal terms. The former describes the one-particle spectrum of an isolated trigonally-distorted CoO 6 octahedron, and key parameters of the local Hamiltonian can be extracted directly from WF [40]. By inspecting different contributions, we find a well-defined hierarchy of energy scales: the strong cubic crystal field (CF), followed by the spin-orbit (SO) interactions, the trigonal CF splitting, and finally, the Zeeman term.…”