“…Moreover, recent advancements in representing external electromagnetic fields, such as recasting Maxwell’s equations in the Schrödinger formalism, , allow for effective and accurate description of light–matter interactions. Thanks to these advantages, grid-based RT-TDDFT finds widespread application in modeling linear and nonlinear optical responses in a broad spectrum of systems, from single atoms, ,,, through clusters ,, and molecules, ,,,− to nanostructures − and solid-state materials. ,,, However, it also has its limitations. For instance, it incorrectly describes single-electron excitations and Rabi oscillations in closed-shell systems , and suffers from the nonlinearity of the time-evolution equations. − Additionally, its significant computational complexity typically restricts the treatment of larger systems at the all-electron level, necessitating the replacement of core electrons with pseudopotentials. ,,, Even with this workaround, the computational cost of RT-TDDFT greatly exceeds that of RT-TDCIS, a drawback shared with more sophisticated multideterminant methods such as real-time time-dependent coupled cluster, ,, RT-TDCISD, ,,,, and RT-TDCIS(D). ,, An alternative approach to RT-TDDFT, proposed by Pauletti et al and also utilized in this work, is to add the exchange–correlation potential directly to the RT-TDCIS Hamiltonian, effectively turning it into the real-time time-dependent counterpart of the Tamm–Dancoff approximation (TDA).…”