Evolutionary Pathways of T-Phase Transition Metal Dichalcogenides: A Comprehensive Study of Pt_<i>x</i>Se_<i>y</i> Clusters

Understanding the transition from nonplanar to planar clusters is crucial for the controllable synthesis of transition metal dichalcogenide (TMDC) monolayers. Using PtSe₂ as a model, we investigate how the chemical environment influences the nucleation and growth stages of monolayer PtSe₂ through structure searching and first-principles calculations. We established a comprehensive database of platinum selenide clusters (Pt_<i>x</i>Se_<i>y</i>, <i>x</i> = 1-10), analyzing 2095 unique clusters and identifying 191 stable isomers and 63 structures with the lowest formation energy on the convex hull. Our findings reveal a chemical environment-dependent phase transition from 3D structures to the planar T-phase of Pt_<i>x</i>Se_<i>y</i> clusters, representing an evolutionary route for PtSe₂ growth. Clusters such as PtSe₆, Pt₂Se₉, Pt₃Se₁₀, and Pt₇Se₁₀ in Pt-rich environments, as well as Pt₂Se₁₅ and Pt₁₀Se₃₂ in Se-rich environments, have been found to exhibit high stability. Additionally, the impact of varying chemical potentials of Pt and Se on the stability of these clusters is explored. PtSe₄ and PtSe₆ are found to be highly stable under most experimentally achievable chemical potential conditions and may serve as dominant precursors during PtSe₂ growth. This work advances our understanding of the nucleation processes of PtSe₂ and other T-phase TMDC materials.