Dresden 2017 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 55: Electronic-Structure Theory: New Concepts and Developments in Density Functional Theory and Beyond - IV

HL 55.9: Talk

Wednesday, March 22, 2017, 12:45–13:00, GER 38

Charged supercells revised: Small Polarons in Oxides with proper account for long-range polarization — •Sebastian Kokott, Sergey V. Levchenko, and Matthias Scheffler — Fritz-Haber-Institut der MPG, Berlin, DE

Formation of small polarons (excess charges localized within one unit cell) often determines charge mobility and optical absorption in oxide materials. In this work, we address two important challenges in the DFT description of small polarons: sensitivity to the errors in exchange-correlation (XC) treatment and finite-size effects in supercell calculations. The polaron properties are obtained using a modified neutral potential-energy surface (PES) [1]. Using the hybrid HSE functional and considering the whole range 0≤ α ≤ 1 of exact exchange, we show that the modified PES model significantly reduces the dependence of the polaron level and binding energy in MgO and TiO₂ on the XC treatment. It does not eliminate the dependence on supercell size. Based on Pekar’s model [2], we derive the proper long-range behavior of the polaron and a correction that allows to obtain the polaron properties in the dilute limit (tested for supercells containing up to 1,000 atoms). The developed approach reduces drastically the computational time for exploring the polaron PES, and gives a consistent description of polarons for the whole range of α. It allows us to find a self-trapped hole in MgO that is noticeably more stable than reported previously.—[1] B. Sadigh et al., PRB 92, 075202 (2015); [2] S.I. Pekar, ZETF 16, 335 (1946). This work received funding from the Leibniz ScienceCampus ”GraFOx“.