In this paper, some electronic properties such as the electronic density of states (DOS), and energy band structure, and optical properties of the bulk and monolayer PtSe2 structure have been investigated based on the density functional theory (DFT) using full-potential linearized augmented plane wave (FP-LAPW) method and the modified Becke-Johnson potential (mBJ). By changing the PtSe2 structure size from bulk to monolayer, there have been major changes in the electronic (DOS and band structure) and optical properties such as the dielectric function. The electronic results show that PtSe2 in the bulk state exhibits a metallic property, while its nanosheet state, PtSe2 is a semiconductor with an energy gap of about 1.5 eV. Band structure calculations showed that for PtSe2 structure in the bulk state the energy distance between Γ-point and the K-point is about 0.4 eV, so it is concluded that PtSe2 is a semi-metal. The optical properties results show that the largest damping region for electromagnetic waves for a bulk PtSe2 structure in the z-direction is equal to 14.02 eV. The volume plasmon energy of the PtSe2 monolayer is smaller than the plasmon energy of the bulk PtSe2. Also, the optical reflectivity of the bulk PtSe2 is larger than the optical reflectivity of the PtSe2 monolayer.
