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B04: Ab-initio theory for photonic materials

M. Sc. Sergej Neufeld
Orthorhombic unit cell of potassium titanyl phosphate (KTP)

M. Sc. Sergej Neufeld, AG Schmidt

My role in project B04
I’m integrated into this project ever since starting my PhD. As a theoretical material scientist, my job involves the characterization of ferroelectrics - mainly lithium niobate (LN) and potassium titanyl phosphate (KTP)- utilized in linear and nonlinear optical applications. That characterization is performed atomistically on the footing of density functional theory (DFT) and includes the determination of linear optical spectra for various levels of theory (DFT, GW, BSE) as well as the influence of defects (point defects, surfaces, etc.) on said spectra. Since the utilized computational methods tend to be computationally rather demanding, I perform my simulations on several super computers in Paderborn (Pling3, Oculus, Noctua) as well as Stuttgart (Hazel Hen).

Quo vadis?
Ultimately, project B04 aims at a deeper understanding of the optical responses of materials on a fundamental, theoretical level. This understanding then hopefully proves to be beneficial to our experimental colleagues in various other project regarding fabrication of optical materials and interpretation of experimental data.

There’s still several open questions to be answered: how do surface reconstructions affect the optical response of KTP? What’s the microscopic origin of color centers (gray tracks) in KTP? How can the experimental Raman spectra of KTP be reconstructed theoretically?

With my calculations, I hope to shed light on several of these questions.