Few-Layer PdSe₂ Sheets: Promising Thermoelectric Materials Driven by High Valley Convergence

Herein, we report a comprehensive study on the structural and electronic properties of bulk, monolayer, and multilayer PdSe₂ sheets. First, we present a benchmark study on the structural properties of bulk PdSe₂ 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 PdSe₂ 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 PdSe₂ sheets, suggesting promising application in thermoelectric cooling.