We calculate the crystal-field splitting, ground-state Kramers doublet and intersite exchange interactions within the ground-state doublet manifold using an ab initio Hubbard-I based approach for a representative set of Ce and Yb triangular-lattice compounds. These include the putative quantum spin liquids (QSL) RbCeO2 and YbZn2GaO5 and the antiferromagnets KCeO2 and KCeS2. The calculated nearest-neighbor (NN) couplings are antiferromagnetic and exhibit noticeable anisotropy. The next-nearest-neighbor (NNN) couplings are ferromagnetic in the Ce systems and dominated by classical dipole-dipole interactions in the Yb case. Solving the resulting effective spin-1/2 models by exact diagonalization up to N=36 sites, we predict ordered magnetic ground states for all systems, including the two QSL candidates. We explore the phase space of an anisotropic NN + isotropic NNN triangular-lattice model finding that a significant antiferromagnetic NNN coupling is required to stabilize QSL phases, while the NN exchange anisotropy is detrimental to them. Our findings highlight a possibly important role of deviations from the perfect triangular model - like atomic disorder - in real triangular-lattice materials.
@article{arxiv.2509.03177,
title = {Ab initio spin Hamiltonians and magnetism of Ce and Yb triangular-lattice compounds},
author = {Leonid V. Pourovskii and Rafael D. Soares and Alexander Wietek},
journal= {arXiv preprint arXiv:2509.03177},
year = {2026}
}