Multistage phase transitions in photoexcited ReS2 monolayer: Real-Time time-dependent density functional theory calculations

Photoinduced phase transitions (PIPTs) allow complex interactions to be distinguished within the constraints of atomic motion. Here, using real-Time time-dependent density functional theory (rt-TDDFT) simulations combined with occupation-constrained density functional theory (DFT) methods, we reveal the ultrafast dynamics of ReS2 monolayer driven by photoexcitation at varying levels of electronic occupancy. The results show that the phase transition from diamond-shaped to zigzag-shaped to quasi-diamond-shaped (DS-ZS-DS′) is effectively induced by 4% excitation manually, resulting in the formation of new quasidiamond chains along the direction of the original diamond chains rotated by π/3. Notably, under pulse excitation, the entire dynamic process also includes subsequent recovery, during which the quasidiamond chains rotate back to their original direction. The phase transition is mediated by the atomic force caused by photoexcited electrons occupying the antibonding state of the Re-Re bonds between the Re4 diamonds, accompanied by the modulation of the potential energy surface. The thermal phonon vibration can effectively reduce the optical excitation fluency required to drive the bond dissociation and rearrangement. These findings provide an important guiding significance for nonequilibrium phase regulation.