Modelling Ferroic Functional Elements

The present study aims at the modelling of an organic field-effect transistor generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods for the microscopic properties of the surface, the molecules, and the respective interactions are combined with classical modelling on the self-assembly of larger adsorbate arrays on a scale-hopping basis. The structural and electronic characteristics of a realistic, stepped titanate surface as well as the electric field strength above such a surface are modelled quantum-mechanically by a combination of density-functional theory (DFT) and density-functional-based tight-binding (DF-TB). The effect of such fields on the electronic and optical properties of polarizable organic molecules is investigated by the time-dependent analogues of the DFT and DF-TB methods. For the integration of organic components via self-assembly a classical Ising Hamiltonian is developped for the coverage of stepped surfaces with molecules and parametrized on the basis of ab-initio and first-principles data.