Revealing the Role of d-Orbital Occupation in Edge Reconstruction of 1T-Transition-Metal Dichalcogenides

ABSTRACT: Despite reports of some possible reconstructed edges of 1T phase-transition-metal dichalcogenides (1T-TMDCs), a global search of 1T-TMDC edge configurations is still absent. A fundamental understanding of the edge formation mechanism and occupation of transition metals, on 1T-TMDC edge reconstruction is still lacking. Here, we proposed a general theoretical framework to understand the edge reconstruction of 1T-TMDCs based on a global search of 1T-TMDC edges and extensive density functional theory calculations. Take freestanding 1T-HfS2 as a prototype of 1T-TMDCs, three edge databases of typical S-terminated zigzag, Hf-terminated zigzag, and armchair edges, including the 33 most stable and 66 metastable edges, are established. We show that the chemical composition and chemical potential heavily affect the appearance of a specific edge. Furthermore, the d-electron occupancy of transition metal at the edge is a fundamental factor dominating the edge stability of various 1T-TMDCs. Two basic types of the most stable edge configurations of various 1T-TMDCs are uncovered. The edge symmetry breaking induces crystal field splitting of transition-metal d orbitals. The reconstructed edges tend to possess an energetically favorable d-orbital occupation. Moreover, a significant indirect-to-direct band gap transition of 1T-TMDCs accompanying edge reconstruction is uncovered. Several reconstructed edges in the databases, especially metastable edges, exhibit excellent catalytic activity in the hydrogen evolution reaction. Our results provide a useful reference for 1T-TMDC edge engineering studies and provide new opportunities for achieving atomic-scale edge control of various 1T-TMDCs.

Automated summary

This study investigates the mechanism and factors influencing the edge reconstruction of 1T-TMDCs, establishes a database of edge configurations, and uncovers the crystal field splitting and band structure transition induced by edge symmetry breaking. The findings have important implications for 1T-TMDC edge engineering and catalytic activity in the hydrogen evolution reaction.