Response-Reformulated TDDFT: An Approach to Strong Field Dynamics With Adiabatic Functionals

Rabi oscillations have traditionally been considered unattainable in simulations using time-dependent density functional theory (TDDFT), highlighting a key limitation of the adiabatic approximation in handling nonperturbative dynamics. We introduce a reformulated approach to TDDFT, RR-TDDFT, for non-equilibrium dynamics that relies solely on response quantities, allowing us to compute nonperturbative electron dynamics with as much confidence as TDDFT is used in the response regime for spectra. The formalism requires the XC functional to be evaluated on a density that remains close to the ground state, rather than on a fully nonperturbative density. RR-TDDFT applies to a wide range of real-time dynamics, significantly enhancing TDDFT's performance beyond equilibrium scenarios. We demonstrate its effectiveness with examples, including a resonantly-driven local excitation in a model helium atom and charge transfer in the LiCN molecule.