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A4: Electronic Ground State and Excited State Properties of complex oxidic Structures

Goal of the project are ab initio investigations of structural, electronic properties as well as excitations of oxidic interfaces and surfaces, the development of new methods for a realistic description of oxides and the assistance of experimental projects.

The ab initio description of oxidic materials requires an efficient and precise treatment of strong correlation effects and the inclusion of experimentally or theoretically determined information on the real structure. The correlation effects will be considered in the framework of the already developed and implemented self-interaction correction (SIC) procedure. Structural information from interfaces and surfaces will be found with efficient pseudopotential methods like VASP.  An intensive cooperation with experimental projects with respect to structural investigations is planned.

Special interest will be devoted to systems with mixed valency. In many oxidic systems atoms can change the valency due to the environment. A characteristic example is the oxide La_1-xSr_xMnO₃. Mn ions will have the valency 3⁺ and 4⁺ to guarantee the neutrality of the system. The valencies of Mn ions can be different in other oxides or at surfaces due to a different chemical environment or symmetry lowering. Therefore, electronic and magnetic properties in the corresponding systems will be influenced strongly by this effect. The valency of the transition metal atoms will be described in an efficient way by the SIC method.

Electronic and magnetic properties and excitations as well will be calculated by means of the Greens function method, which is implemented in the code HUTSEPOT. The code HUTSEPOT allows efficient ab initio investigations of complex real structures in different dimensions and combines methods, inevitable for the treatment of oxidic systems. Structural and magnetic defects will be taken into account by means of the coherent potential approximation (CPA). Adiabatic and dynamic magnetic properties will be realistically described using the magnetic force theorem and dynamic linear response theory. Excitation properties can be calculated in the framework of the GW method. This method will be combined with self-interaction corrections. In the next period the code will be extended to a fully relativistic description (Dirac equation) of the electronic structure. SIC, the magnetic force theorem, and the dynamic linear response theory will be included  in the relativistic theory.

Principal Investigators

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