Seminarium "Modeling of Complex Systems"

Two-dimensional (2D) materials have received a lot of attention in recent years. Moreover, the physical properties of 2D materials have been studied extensively with density functional theory (DFT). Due to the strong light- matter interaction, many-body methods beyond DFT are usually needed to describe the optical properties of 2D systems accurately. These meth-ods are often computationally demanding. In this work, we compute optical absorbance spectra for several 2D materials using a recently developed method based on time-dependent density functional theory (TD-DFT) and the HSE06 hybrid functional. This method (TD-HSE06) turns out to be faster than the standard many-body methods. With a test set of eight common 2D materials, we show that the TD-HSE06 method results in optical absorbance spectra that are in agreement with recent experimental and computational studies. In addition, the errors of the optical gaps determined with the TD-HSE06 method are rather small compared with the many-body calculations. We also calculate the TD-HSE06 optical absorbance spectra for transition metal carbides called MXenes. Our calculations show that the TD-HSE06 method makes it possible to describe the optical gaps and optical absorbance spectra of 2D materials quite accurately. Furthermore, the TD- HSE06 method can also describe excitons in 2D materials whereas standard spectrum calculations neglect the excitons completely.