Origin of distorted 1T-phase ReS₂: first-principles study

Group-VIIB transition metal dichalcogenides (TMDCs) are known to be stabilized solely in a distorted 1T phase termed as 1T″ phase, which is compared to many stable or metastable phases in other TMDCs. Using first-principles calculations, we study the structural origin of 1T″ phase group-VIIB TMDCs. We find that quasi 1D Peierls-like instability is responsible for the transition to the 1T″ phase ReS₂ monolayer from the 1T' phase, another distorted 1T phase. Two half-filled bands in 1T'-ReS₂ make sharp peaks in the Lindhard function that prompt the charge density wave (CDW) phase with large band gap opening. Our calculations show that overlapping of the two bands in a broad energy range leads to robust CDW phase or stable 1T″ phase in group-VIIB TMDCs against compositional variation, which is in stark contrast to typical Peierls instability driven by a single band. Calculated total energy curve near the critical point exhibits the feature of the first-order Landau transition due to local chemical bonding. The structural stability of the 1T″ phase in group-VIIB TMDCs is thus guaranteed by two half-filled bands and local chemical bonding.