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Here, we investigated the interrelationship between pressure and correlation in the LaFeAsO compound by the density functional theory method combined with the dynamical mean field theory (DFT+DMFT) method. The spectral function and the occupation number (ON) of Fe-3d orbitals at different pressures were extracted from the calculations, and the importance of the role of correlation in superconductivity in iron-based compounds was indicated. The measured ON of Fe-3d orbitals demonstrated charge transfer between them and also the crucial role of the Fe-3dxy (xy) orbital in superconductivity in these materials. A switching behavior between high and low TC through decreasing the correlation was observed in our calculations, originating from the orbital switching. This shows the significant role of the orbital degrees of freedom in iron-based superconductors.

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Electronic and magnetic properties of the heavily H-doped LaFeAsO1−xHx (x ∼ 0.5) were studied in the framework of the density functional theory combined with the dynamical mean field theory (DFT+DMFT). We found a stripe-like-ordered structure of hydrogen and oxygen atoms, as a ground state, with the same configuration as the antiferromagnetic (AF) order. The new configuration could explain the existing experimental results related to the heavily H-doped LaFeAsO1−xHx, such as an in-plane electronic anisotropy and a non-uniform magnetic behavior. A significant anisotropy was observed between Fe-3dxz (xz) and Fe-3dyz (yz) orbitals in the ground state in the absence of the pseudogap resulting from the spin density wave phase, which was found to originate from the crystalline anisotropy. Magnetic moments were not spatially uniform and were sensitive to the crystal configuration. We found that a non-uniform magnetic behavior is associated with the As-Fe-As bond angle in the structure. Our findings would clarify the importance of crystal details and orbital degrees of freedom in iron-based superconductors. * Electronic address: mehdi.hesani@gmail.com

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