A influência da configuração de empilhamento nas propriedades estruturais, energéticas e optoeletrônicas da bicamada de PdX2 (X = S, Se, Te)

Abstract

This work presents a first-principles investigation into the influence of stacking configuration on the structural, energetic, and optoelectronic properties of bilayer palladium dichalcogenides PdX2 (where X = S, Se, Te). The central objective is to analyze how different interlayer stacking patterns modulate the stability, electronic structure, and work function of these two-dimensional materials. The methodology employs computational simulations based on Density Functional Theory using the VASP software, describing the core-valence electron interactions via the projector augmented-wave method. The study uses the semilocal PBE functional for structural optimizations, obligatorily incorporating Grimme’s D3 correction for the rigorous treatment of van der Waals dispersion forces, which are fundamental elements for the stabilization of lamellar interfaces. For the refinement of the band structure and work functions, the research applies the HSE06 hybrid functional, ensuring greater accuracy in determining the band gap. The results indicate that the bulk-like configuration represents the global minimum energy state for the three investigated systems, serving as an absolute reference for stability. It is observed that the binding energy becomes progressively more negative in the sequence S → Se → Te, which reflects the increase in polarizability and the spatial extent of the electronic orbitals in the heavier atoms. The work demonstrates that PdS2 preserves its indirect band gap semiconductor character across all tested stackings, although the spatial organization significantly alters the electronic occupations near the band edges and induces a pronounced in-plane optical anisotropy for polarized light. In the PdSe2 system, stacking acts as a trigger for electronic phase transitions, allowing the material to transition between semiconductor, semimetallic, and metallic behaviors depending on the adopted geometry. Conversely, PdTe2 consistently maintains its metallic nature regardless of the stacking pattern, although it exhibits variations in the density of states and in the band crossings at the Fermi level. Bader charge analysis reveals that the stacking primarily perturbs the interfacial chalcogen atoms, establishing electric dipoles that shape the surface electrostatics. The work function exhibits a systematic reduction with the increase in chalcogen mass, but allows for additional fine-tuning through stacking engineering. The work concludes that the stacking configuration constitutes a practical and effective tuning parameter for the design of nanodevices. The detailed understanding of these mechanisms provides a theoretical foundation for the development of optoelectronic technologies and for contact engineering in two-dimensional materials.