# Accounting for Electronic Coherences Induced by Broadband Pulses by Using Pulse-Independent Trajectories

## TL;DR

This paper introduces new methods to model the effects of laser pulses on molecular dynamics without recalculating for each pulse, improving efficiency and accuracy in simulations.

## Contribution

The paper presents two trajectory-surface-hopping approaches that account for pump-generated coherences without requiring separate calculations for each pulse.

## Key findings

- The new methods show excellent agreement with simulations that include coherences from the start.
- Initial coherences play a significant role in early nonadiabatic dynamics in glycine molecules.
- The approaches enable accurate and flexible simulations for pump–probe experiments with broadband laser sources.

## Abstract

Recent advances in the generation of ultrashort, few-femtosecond
laser pulses in the ultraviolet–visible domain are now enabling
the coherent excitation of several electronic states in neutral molecules,
with new opportunities for the manipulation of molecular dynamics
on ultrafast time scales. Current time-resolved pump–probe
experiments can monitor the ensuing coupled electron–nuclear
dynamics with ultrashort resolution. Computational modeling of the
observables measured in such experiments can be very challenging for
medium-sized and large molecules because of (i) the nontrivial treatment
of pump-generated coherences with mixed quantum–classical methods
and (ii) the high computational cost of probe-step calculations, which
cannot be afforded when many different pump pulses have to be considered,
as e.g., in control schemes. In this work, we present two trajectory-surface-hopping
approaches that include, a posteriori, the effect
of the pump-generated coherences on the ensuing coupled electron–nuclear
dynamics, thus avoiding performing a different coupled electron–nuclear
dynamics calculation for every individual pump pulse. The effectiveness
of both approaches is exemplified in glycine molecules excited by
short ultraviolet pump pulses. We compare the results of both approaches
with those obtained by including pump-generated coherences from the
very beginning, showing an excellent agreement and confirming the
important role of such initial coherences in the early nonadiabatic
dynamics. Our results pave the way for both accurate and flexible
simulations of pump–probe experiments or control studies in
molecules excited by broadband laser sources.