Dresden 2014 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 58: Oxide and Insulator Surfaces II
O 58.7: Vortrag
Mittwoch, 2. April 2014, 17:30–17:45, PHY C 213
Stability and Metastability of Clusters in a Reactive Atmosphere: Theoretical Evidence for Unexpected Stoichiometries of MgMOx — •Saswata Bhattacharya, Sergey V. Levchenko, Luca M. Ghiringhelli, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin
We study the (meta)stability of metal-oxide clusters in a reactive atmosphere at thermodynamic equilibrium, using free metal (Mg) clusters in an oxygen atmosphere as a model system. The low energy minimum structures of a large set of MgMOx clusters are generated via a massively parallel cascade genetic algorithm. The term “cascade" means a multi-step procedure with increasing accuracy and each next level uses information obtained at the immediate lower level. It starts with a (reactive) force field and goes up to density-functional theory (DFT) with hybrid functionals. The stable compositions are identified using ab initio atomistic thermodynamics. We find[1] that highly oxidised states are more stable at thermodynamic equilibrium when M ≤ 5, while for bigger sizes (6 ≤ M ≤ 15) there is a competition between stoichiometric (x = M) and non-stoichiometric (x > M) clusters. The highly oxidised clusters (x > M) exhibit peculiar magnetic behaviour, suggesting the possibility of tuning magnetic properties by changing environmental (T,pO2) conditions. Our studies are validated with the highest level currently achievable within DFT, i.e.; the renormalized second-order perturbation theory (rPT2).
[1] S. Bhattacharya, S. V. Levchenko, L. M. Ghiringhelli, M. Scheffler, Phys. Rev. Lett. 111, 135501 (2013)