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Influence of strain on the properties of CeRuPO and CeOsPO Kondo systems

We investigated the influence of isotropic strain on the type of the magnetic ground-state and the Fermi surface for the structurally-equivalent CeRuPO and CeOsPO crystals with slightly different lattice parameters. The two systems exhibit different magnetic orderings at zero strain. According to the phase diagram of CeRuPO under pressure the difference might be due to the different Ce-Ce inter-atomic distances. We applied {\it ab-initio} calculations based on the density-functional theory and the generalized-gradient approximation with an additional Coulomb repulsion (GGA+$U$), which indeed reveal a significant impact of the strain and the effective $U$ parameter on the magnetic ground state. However, it is demonstrated that the difference is more likely related to the details in the Fermi surface.