Resolving contradictory estimates of band gaps of bulk PdSe2: A Wannier-localized optimally-tuned screened range-separated hybrid density functional theory study

Palladium diselenide (PdSe2)—a layered van der Waals material—is attracting significant attention for optoelectronics due to the wide tunability of its band gap from the infrared through the visible range as a function of the number of layers. However, there continues to be disagreement over the precise nature and value of the optical band gap of bulk PdSe2, owing to the rather small value of this gap that complicates experimental measurements and their interpretation. Here, we design and employ a Wannier-localized optimally tuned screened range-separated hybrid (WOT-SRSH) functional to investigate the electronic band structures and optical absorption spectra of bulk and monolayer PdSe2. In particular, we account carefully for the finite exciton center-of-mass momentum within a time-dependent WOT-SRSH framework to calculate the indirect optical gap and absorption onset accurately. Our results agree well with the best available photoconductivity measurements, as well as with state-of-the-art many-body perturbation theory calculations, confirming that bulk PdSe2 has an optical gap in the mid-infrared (upper bound of 0.44 eV). More generally, this work further bolsters the utility of the WOT-SRSH approach for predictive modeling of layered semiconductors.