Berlin 2015 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 80: Challenges in semiconductor theory

HL 80.3: Vortrag

Donnerstag, 19. März 2015, 15:30–15:45, EW 015

Hybrid density-functional calculations of polarons in doped MgO. — •Sebastian Kokott, Sergey Levchenko, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

Charge-carrier conductivity in oxides can influence their surface chemical properties [1]. However, the nature and properties of the charge carriers are not well understood. In this work, we investigate self-trapped polarons in MgO within an ab initio framework. Density-functional theory with the hybrid functional HSE06 is used for the atomic relaxtion and electronic structure calculations. The choice of the functional is validated by the analysis of the (de)localization bias according to the generalized Koopmans’ condition [2] as a function of the fraction of Hartree-Fock exchange. We find a localized polaronic distortion of the MgO lattice which was not reported previously: two neighboring oxygen atoms forming an O₂²⁻ moiety with two trapped electronic holes. We do not find a self-trapped state for a single hole with the HSE06 functional. The formation energy of the polaron is about 1 eV, i.e., thermally accessible at typical temperatures when p-doped MgO is used as a catalyst (800-1,000 K) [3]. We also explore polarons trapped at intrinsic and extrinsic point defects, in particular Mg vacancies and hydrogen intersitials. [1] Richter et al., Phys. Rev. Lett. 111, 045502 (2013); [2] Lany and Zunger, Phys. Rev. B 80, 085202, (2009); [3] Arndt et al., Catalysis Rev. 54 (4), 424-514 (2011).