Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 39: Focussed session: Theory and computation of electronic structure: new frontiers III (jointly with HL, DS)

O 39.4: Vortrag

Mittwoch, 16. März 2011, 12:00–12:15, TRE Phy

Ab-initio study of MnO and NiO in various crystal structures – The failure of (semi)local density functionals — •Andreas Schrön, Claudia Rödl, and Friedhelm Bechstedt — IFTO, FSU Jena, Max-Wien-Platz 1, 07743 Jena, Germany

Transition-metal oxides (TMOs) are of great interest for applications in e.g. dilute magnetic semiconductors (DMSs) which are supposed to allow for transparent ferromagnets with high critical temperatures. One of the most promising host materials is ZnO which crystallizes in the wurtzite structure. Although TMOs have been investigated a long time experimentally, their theoretical description is still unsatisfying.

The semilocal generalized-gradient approximation (GGA) to density functional theory (DFT) works well for many materials. Here we demonstrate that this approach predicts the wrong ground-state crystal structure for MnO, since it does not account sufficiently for the electron correlation effects in materials with strongly localized electrons. It is usually assumed, that approaches including an additional on-site Coulomb interaction U (GGA+U) or non-local exchange contributions like the hybrid functional HSE03 cure this failure.

The relative energetic ordering of the rock-salt, zinc-blende, and wurtzite crystal structures are investigated for various magnetic orderings. It is shown that neither GGA nor the HSE03 hybrid functional yields the experimentally observed ground-state structure. However, agreement with experiment is obtained if the GGA+U functional with U > 4 eV is applied. For NiO, on the other hand, all three functionals yield rock-salt as the equilibrium crystal structure.