Coulomb parameters are key for understanding the exchange mechanism in magnetic materials. In this work, we investigate the reasonable Coulomb parameters in the proposed candidate of Kitaev material CoTiO3. Applying the constrained random-phase approximation (cRPA) method, we specify the lower limit of the direct Coulomb interaction U and the upper limit of Hund's rule exchange JH. Adopting the cRPA Coulomb parameters combined with the material-specific hopping parameters, we calculate the d-d superexchange couplings in CoTiO3 by the many-body perturbation theory. We show that the d-d superexchanges are insufficient to interpret the dominant ferromagnetic couplings in CoTiO3. Therefore other contributions, e. g. , charge-transfer related processes, are necessary.
Wang et al. (Thu,) studied this question.
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