Study of electron thermalization under intense laser pulse on monolayer graphene using real-time TDDFT

Thermalization behavior at extreme temperatures is of utmost importance in understanding how materials behave when exposed to high-intensity lasers. This is truly a non-linear phenomenon and traditional perturbative approaches fail. This work explores how real-time Time-Dependent Density Functional Theory (rt-TDDFT) can thermalize electronic states and how those thermal states are represented. Using the Octopus code, we investigate how monolayer graphene behaves under laser excitation. In the linear regime, graphene is known to absorb πα (~2.3) percent of incident energy [R. R. Nair et al. Science 2008, 320, 1308-1308]. We determine the boundary between linear and nonlinear absorption regimes for the pulse intensity from the amount of energy gained by the monolayer from the laser. We also calculate the distribution of occupations over time by projecting time-evolved wavefunctions onto the ground-state wavefunctions. We look at the nature of thermalization in TDDFT by comparing how close this distribution comes to resembling the Fermi-Dirac distribution over time. The results provide insights into the timescales and mechanisms governing thermalization in graphene, contributing to a deeper understanding of energy transport in two-dimensional materials under high-energy-density conditions.