We use real-time electronic structure methods, typically real-time time-dependent density functional theory (RT-TDDFT). RT-TDDFT is a density-functional-based approach to electronic excited states which solves the time-dependent Kohn-Sham equations by propagating the wavefunction or density matrix in real-time.
Although it shares many of the limitations of traditional linear-response TDDFT, RT-TDDFT yields a full time-resolved, potentially non-linear solution. Real-time simulations can be used to compute not only spectroscopic properties (e.g., absorption spectra, polarizabilites, etc), but also the time and space-resolved electronic response to arbitrary external stimuli (e.g., electron charge dynamics after laser excitation).