Effects of the Oxidation States of 3d Elements on the Electronic Properties of Ho₂CoCrO₆
Description
The electronic structure of the double perovskite Ho2CoCrO6 is investigated using density functional theory within the GGA+U framework. Structural descriptors, including the tolerance factor, global instability index, and bond-valence analysis, indicate that monoclinic P2₁/n configurations with a⁻b⁺a⁻ octahedral tilting are chemically favorable. The influence of oxidation-state models is examined through three nominal Co/Cr configurations (Co2+/Cr4+, Co3+/Cr3+, and Co4+/Cr2+).
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Steps to reproduce
Band structure and density of states calculations for the Ho2CoCrO6 material were carried out assuming a monoclinic crystal structure with space group P21/n (#14), considering different combinations of oxidation states for the cobalt and chromium atoms: Co2+/Cr4+, Co3+/Cr3+, and Co4+/Cr2+. The electronic properties were investigated using first-principles calculations based on density functional theory (DFT). To describe the core-electron interaction, the Projector Augmented Waves (PAW) [32-33] method was used, as implemented in the VASP code [34]. The interaction between exchange and correlation was treated using the Generalized Gradient Approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional [35]. Since the structure contains transition cations with 3d orbitals, the Hubbard correction (GGA+U) was applied to improve the description of local electronic correlation effects. Values of UCr=3.7 eV and UCo=3.32 eV were established, the suitability of which has been supported by previous studies [21]. The plane waves expanded with a cutoff energy of 550 eV, ensuring high precision in total energy, with variations of less than 0.001 eV per atom. Integration in reciprocal space was performed using the Monkhorst-Pack scheme, with a 9×9×7 k-point grid [36], allowing energy convergence to be achieved with fluctuations of less than 1 meV per atom. Partial occupations of electronic states near the Fermi level were treated using the Methfessel–Paxton smearing method with a width of 0.05 eV [37]. Finally, complete structural optimization was performed, simultaneously relaxing the network parameters and atomic positions until the residual forces on all ions were less than 30 meV/Å. These conditions ensured the attainment of a well-converged and favorable structural and electronic configuration, representative of the crystalline equilibrium state.
Institutions
- Universidad Nacional de ColombiaBogota D.C., Bogotá