First-principles investigation of the relationship between laser irradiation intensity and non-thermal melting of <i>α</i>-quartz

Non-thermal melting induced by femtosecond laser irradiation has been widely studied. Previous simulations typically relied on thermally equilibrated electronic systems within the Born–Oppenheimer approximation. However, this method overlooks the stepwise nature of electronic excitation caused by laser pulses and assumes that the electronic system remains in equilibrium throughout. To address these limitations, the relationship between femtosecond laser irradiation and non-thermal melting in α-quartz was analyzed using time-dependent density functional theory. The results show that non-thermal melting can be effectively characterized by the fraction of excited electrons. Moreover, to mitigate the typical underestimation of the bandgap in simulations, a correction was applied using the meta-generalized gradient approximation (GGA) functional. This adjustment enables more accurate estimates of laser absorption in the low-temperature regime and highlights that the conventional GGA functional tends to overestimate laser absorption. The findings may inform parameter selection in laser processing applications and improve predictions of the mass transfer rates.