Accurate calculation of excitonic signatures in the absorption spectrum of BiSBr using semiconductor Bloch equations

In order to realize the significant potential of optical materials such as metal halides, computational techniques which give accurate optical properties are needed, which can work hand-in-hand with experiments to generate high efficiency devices. In this work a computationally efficient technique based on semiconductor Bloch equations (SBEs) is developed and applied to the material BiSBr. This approach gives excellent agreement with the experimental optical gap, and also agrees closely with the excitonic stabilisation energy and the absorption spectrum computed using the far more computationally demanding ab initio Bethe-Salpeter approach. The SBE method is a good candidate for theoretical spectroscopy on large- or low-dimensional systems which are too computationally expensive for an ab initio treatment.