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Doping dependence of antiferromagnetism in models of the pnictides

We study the doping dependence of the spin-density-wave (SDW) state in four models of the 1111 pnictides. The random-phase approximation is used to determine the ordering temperature and the ordering vector as functions of doping, and to evaluate the contribution of the various orbitals to the SDW instability. In addition to the usual assumption of orbitally rotation-invariant interactions, we consider the effect of reduced interactions involving the xy orbital, which are anticipated by crystal-structure considerations. We find that changing the relative strength of the interaction in the xy orbital tunes the system between different nesting instabilities leading to similar SDW order. We identify two models as showing reasonable agreement with experiments, while the other two display significant discrepancies, and discuss the underlying differences between the models.