Investigating Size-Dependent Accuracy of Real-Time Time-Dependent Density Functional Theory

Real-time time-dependent density functional theory (RT-TDDFT) has been used to simulate electronic response properties (e.g., ionization, charge transfer) within one of the most widespread approximations within RT-TDDFT: temporal adiabaticity, i.e. the adiabatic approximation. However, for small systems, RT-TDDFT within the adiabatic approximation can lead to incorrect charge transfer. The size-dependency of this popular approximation is not well-understood. By comparing RT-TDDFT densities to those obtained via time-dependent configuration interaction methods, this work attempts to elucidate the relation between system size and the applicability of RT-TDDFT in modeling charge transfer.