Few-Layer PdSe(2) Sheets: Promising Thermoelectric Materials Driven by High Valley Convergence

[Image: see text] Herein, we report a comprehensive study on the structural and electronic properties of bulk, monolayer, and multilayer PdSe(2) sheets. First, we present a benchmark study on the structural properties of bulk PdSe(2) by using 13 commonly used density functional theory (DFT) functionals. Unexpectedly, the most commonly used van der Waals (vdW)-correction methods, including DFT-D2, optB88, and vdW-DF2, fail to provide accurate predictions of lattice parameters compared to experimental data (relative error > 15%). On the other hand, the PBE-TS series functionals provide significantly improved prediction with a relative error of <2%. Unlike hexagonal two-dimensional materials like graphene, transition metal dichalcogenides, and h-BN, the conduction band minimum of monolayer PdSe(2) is not located along the high symmetry lines in the first Brillouin zone; this highlights the importance of the structure–property relationship in the pentagonal lattice. Interestingly, high valley convergence is found in the conduction and valence bands in monolayer, bilayer, and trilayer PdSe(2) sheets, suggesting promising application in thermoelectric cooling.