  Time-resolved spectroscopy is an important tool for unraveling the minute
details of structural changes of molecules of biological and technological
significance. The nonlinear femtosecond signals detected for such systems must
be interpreted, but it is a challenging task for which theoretical simulations
are often indispensable. Accurate simulations of transient-absorption or
two-dimensional electronic spectra are, however, computationally very
expensive, prohibiting the wider adoption of existing first-principles methods.
Here, we report an AI-enhanced protocol to drastically reduce the computational
cost of simulating nonlinear time-resolved electronic spectra which makes such
simulations affordable for polyatomic molecules of increasing size. The
protocol is based on doorway-window approach for the on-the-fly surface-hopping
simulations. We show its applicability for the prototypical molecule of
pyrazine for which it produces spectra with high precision with respect to ab
initio reference while cutting the computational cost by at least 95% compared
to pure first-principles simulations.
