Anisotropic intersite exchange interactions in frustrated rare-earth magnets are difficult to assess both theoretically and experimentally. Here, we propose an ab initio force-theorem framework combining the quasi-atomic Hubbard-I approach to 4f correlations with a static mean-field treatment of the on-site intershell Coulomb interaction between rare-earth 4f and 5d states to simultaneously capture both 4f superexchange and 5d-mediated indirect exchange. Applying it to the triangular lattice Ce delafossites CsCeSe2, KCeS2, and RbCeO2, we find that the indirect exchange dominates in the selenide, the superexchange in the oxide, while both mechanisms contribute almost equally in the sulfide. The magnetic exciation spectra of CsCeSe2 and KCeS2 evaluated from the calculated spin Hamiltonains are in good qualitative and quantitative agreement with experimental data.
@article{arxiv.2511.14904,
title = {5d-mediated indirect exchange and effective spin Hamiltonians in Ce triangular-lattice delafossites},
author = {Leonid V. Pourovskii},
journal= {arXiv preprint arXiv:2511.14904},
year = {2026}
}