Theoretical investigation of the electronic structure and magnetic properties of Ru doped LiFeAs.

This study performed first-principles calculations using Density Functional Theory (DFT) and DFT+U within the Quantum-Espresso package. . The electronic structure and magnetic properties of Ru-doped LiFeAs were systematically analyzed at doping concentrations of 25%, 50%, and 100%, revealing significant modifications induced by Ru substitution. The optimized lattice parameter of pristine LiFeAs is 3.767 Å, in excellent agreement with the experimental value of 3.77 Å. Upon 25% Ru substitution, the lattice parameter expands slightly to 3.786 Å, reflecting the structural response to partial Ru incorporation. The computed electronic structure and magnetic properties of LiFe1-xRuxAs confirm its metallic nature, with no detectable band gaps. Density of States (DOS) calculations reveal that the conduction band near the Fermi level is primarily dominated by Fe-3d and Ru-4d orbitals, while the valence band is largely influenced by As-p states. With 25% Ru substituted, the electronic band structure shows a strong buildup of states close to the Fermi level, suggesting that the material is becoming more metallic. This elevated electronic density at the Fermi surface is likely to have a substantial impact on the material's superconducting behavior and charge transport properties, potentially enhancing its conductivity and modifying the electron pairing interactions. In the ferromagnetic (FM) configuration, Ru doping enhances both spin polarization and metallicity, whereas the antiferromagnetic (AFM) state exhibits a suppressed DOS near the Fermi level. The inclusion of the Hubbard U correction provides improved insight into localized electron interactions, particularly in the Fe 3d orbitals. This study contributes to a deeper understanding of the interplay between doping, electronic correlation, and magnetism in iron-based superconductors. The pristine, 25, and 50% Ru-doped LiFeAs systems retain AFM coupling, while full (100%) Ru substitution induces a transition to a nonmagnetic state. The magnetic moments of Fe atoms decrease progressively with increasing Ru concentration, indicating a suppression of magnetism.