Photoinduced amorphization in chalcogenide phase-change materials plays a key role in enabling ultrafast photonic functionality. Here, real-time time-dependent density-functional theory simulations are employed to elucidate the microscopic mechanism of ultrafast amorphization in ${\mathrm{Sb}}_2{\mathrm{Se}}_3$ under femtosecond laser excitation. The results reveal that the occupation of Sb–Se antibonding states weakens the covalent network and initiates local melting that develops into a percolated amorphous structure. At low temperature, coherent phonons drive ordered Peierls-like distortions, whereas thermal phonons at room temperature disrupt coherence and accelerate structural disorder. By incorporating a Boltzmann factor $\tau$ to restore detailed balance, the simulations capture hot-carrier cooling and electron-phonon energy transfer. This approach reveals the intrinsic correlation among photoexcitation, energy relaxation, and structural evolution, offering microscopic insight into ultrafast phase transitions.

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• Density of states
• Phase-change materials
• Photoinduced effect
• Semiconductor compounds
• Density functional theory