Optical excitations in 2D semiconductors

Two-dimensional (2D) materials have revealed many fascinating physical and chemical properties. Due to the quantum confinement and enhanced many-body effects especially the optical properties are altered compared to their bulk counterparts. The optics of 2D materials can easily be modified by various means, e.g. the substrate, doping, strain, stacking, electric or magnetic fields. In this review we focus on the theoretical description of the excited states and optical properties of 2D semiconductors paying particular attention to the current challenges and future opportunities. While the presented methodology is completely general and applicable to any 2D material, we discuss results for the transition metal dichalcogenides, their heterostructures, and some novel materials from the computational 2D materials database.