Regensburg 2016 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 62: Methods in Computational Materials Modelling IV: Method development

MM 62.4: Vortrag

Donnerstag, 10. März 2016, 16:30–16:45, H53

Hybrid-functional calculations of iron defects in ferropericlase — •Sebastián Alarcón Villaseca, Sergey V. Levchenko, and Matthias Scheffler — Fritz-Haber-Institut der MPG, 14195 Berlin, DE

The accurate description of transition-metal-containing defects in crystals presents a challenge for DFT with standard LDA and GGA functionals. Although replacing a fraction α of the (semi-)local exchange by the exact exchange (EX) in hybrid DFT reduces the self-interaction error, α remains a parameter depending on the target property. Here, the dependence of the formation energies of Fe_Mg substitutional defects in ferropericlase (Mg,Fe)O - the second most abundant mineral in Earth’s lower mantle - on α in the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) (0 ≤ α ≤ 1, α = 0 corresponds to PBE) is explored, and the results are compared to CCSD(T) embedded cluster calculations. We find that HSE(α = 0.48) reproduces the formation energy obtained with CCSD(T) and satisfies the constraint that the DFT HOMO equals the ionization energy as calculated by G₀W₀@HSE(α). Periodic models with converged unit-cell size are then used to calculate the atomic and electronic structure of Fe_Mg substitutional defect in MgO. The O_h → D_4h symmetry lowering (compressed FeO₆ octahedron) derived from experiments [1] is found for all α values (with HSE(α = 0.25) lattice parameter). However, the negative Δt_2g splitting of the Fe 3d states is obtained only for α ≥ 0.4. The calculated Δt_2g at these α values indicate a dynamic Jahn-Teller effect [1].

[1] T. Hauptricht et al., Phys. Rev. B 82, 035120 (2010).