Methods

We work mostly with density functional theory (DFT) based approaches for the investigation of semiconductors. It is well known that plain DFT severely underestimates bandgaps and that more accurate values are obtained with either hybrid functionals or GW many-body approaches. However, these approaches are available at a large computational costs and cannot always be used for the large systems we consider such as layered halide perovskites that requires large and sparse simulation cells. For that reason, we are looking for cheapest way to access a more accurate picture of the electronic structure of the materials, such as the so-called DFT-1/2 scheme or the Tran-Blaha modified Becke-Johnson potential.

The investigation of the dielectric properties of semiconductors and their interfaces requires the ability to calculate the dielectric constant profile along the interface direction (ε(z)). Together with L. Pedesseau (Institut FOTON) and J. Even (Institut FOTON) we proposed a computational approach much less demanding based on DFT calculations using local basis sets as implemented in the SIESTA code. It has since been applied to colloidal nanoplatelets of CdSe passivated by acetate molecules as well as halide perovskites. The approach has been completed by the evaluation of the self-energy correction profiles.

The standard computational approach to describe electron-hole pairs involves the use of many-body perturbation theory within the GW scheme followed by the resolution of the Bethe-Salpeter equation (BSE). However, this process is computationally extremely demanding and often non applicable to the large structures we are mostly interested in. For that reason, we use a semi-empirical resolution of the BSE using ingredients taken either from DFT calculations or from experimental data. In particular, we applied this approach with success to different layered halide perovskites.