Optimizing optical properties of bilayer PtSe2: The role of twist angle and hydrostatic pressure

Two-dimensional van der Waals materials offer exceptional tunability in their electronic properties. In this paper, we explore how twisting and hydrostatic pressure can be leveraged to engineer the electronic and optical characteristics of bilayer PtSe2. Using state-of-the-art first-principles density functional methods, we calculate the electronic band structure and the imaginary part of the dielectric function across multiple twist angles and pressure values. We find, that at the twist angle θ=13.17°, bilayer PtSe2, which is intrinsically an indirect semiconductor, transforms into a direct-gap semiconductor. Moreover, we demonstrate that hydrostatic out-of-plane pressure boosts near-infrared optical activity, further expanding the functional potential of PtSe2 bilayers. The demonstrated high tunability of electronic and optical properties by twisting and pressure opens new application directions of PtSe2 in optoelectronics.