PULSE-PySpawn: Time-Resolved Transient Absorption Simulation through Ab Initio Multiple Spawning Dynamics with Explicit Pulses

We report a new workflow to model time-resolved transient
absorption
spectra based on propagating non-adiabatic dynamics with ab
initio multiple spawning. By explicitly including a laser
field in the molecular Hamiltonian, we can model both the effect of
a pump pulse in depopulating the ground state and a series of probe
pulses to monitor the evolution of the nuclear density. We developed
a flexible and efficient workflow that enables the inclusion of probes
of different energies at different time delays, matching real experimental
conditions. In this way, we are able to reconstruct the spectroscopic
signal from a single set of trajectories. We included our workflow
in the open-source code PySpawn to exploit all of the implementations
recently added to this software and to ensure wider usability of our
method. Finally, we showed the applicability and strength of our development
in simulating and interpreting the time-resolved transient absorption
spectrum of azomethane.