Real-time simulation of charge migration within the time-dependent Kohn–Sham DFT

Attosecond technologies provide unique opportunities to study electron dynamics and electron correlation on their intrinsic timescales. From a theoretical perspective, this places strong constraints, as an accurate treatment of electron correlation is required. Recently, it was demonstrated that time-dependent density-functional theory (TDDFT) is capable of correctly predicting correlation-driven charge migration arising from hole mixing following ionization of the highest occupied molecular orbital (HOMO). Given the ability of TDDFT to treat large-scale systems, this approach offers promising perspectives for investigating electron-correlation-driven mechanisms in complex molecules. In this work, we assessed the constraints and limitations associated with using TDDFT to study this mechanism. We found that the charge-migration dynamics are already correctly reproduced using the local-density approximation for the exchange-correlation functional, provided the states involved in the coherent superposition are well described within TDDFT. However, for dynamics triggered by the ionization of orbitals below the HOMO, artificial ultrafast dynamics may appear on top of the charge-migration dynamics. These artifacts indicate that careful analysis of the simulated dynamics is required to reliably predict phenomena that could be observed experimentally.