Thickness Dependent Electronic Structures of Pd Dichalcogenides: A First Principles Study*

Among the family of transition metal dichalcogenides (TMDs), Pd-based TMDs have been one of the less explored materials. In this study, using first-principles calculations, we investigate the electronic properties of PdX₂ (X=S, Se, or Te) with respect to film thickness. With regards to the structural stability, the bulk and thin film structures of PdS₂ and PdSe₂ exhibit pyrite phase, while PdTe₂ exhibits 1T phase as their most stable configurations. For the electronic properties, the most stable bulk configurations demonstrate semi-metallic features, while their corresponding monolayer structures for pyrite PdS₂ and PdSe₂ are insulating with band gaps of 1.399 eV and 1.548 eV, respectively, while 1T PdTe₂ remained to be semi-metallic. For the band properties, we observe that all these materials manifest decreasing/closing of indirect band gap with increasing thickness. Moreover, all the stable monolayer band structures exhibit flat bands and diverging density of states near the Fermi level, indicating the presence of van Hove singularity.