Simulating Ultrafast Transient Absorption Spectra from First Principles using a Time-Dependent Configuration Interaction Probe
arxiv(2024)
摘要
Transient absorption spectroscopy (TAS) is among the most common ultrafast
photochemical experiments, but its interpretation remains challenging. In this
work, we present an efficient and robust method for simulating TAS signals from
first principles. Excited-state absorption and stimulated emission (SE) signals
are computed using time-dependent complete active space configuration
interaction (TD-CASCI) simulations, leveraging the robustness of time-domain
simulation to minimize electronic structure failure. We demonstrate our
approach by simulating the TAS signal of
1^'-hydroxy-2^'-acetonapthone (HAN) from ab initio multiple
spawning nonadiabatic molecular dynamics simulations. Our results are compared
to gas-phase TAS data recorded from both jet-cooled (T∼ 40 K) and hot
(∼ 403 K) molecules via cavity-enhanced transient absorption spectroscopy
(CE-TAS). Decomposition of the computed spectrum allows us to assign a rise in
the SE signal to excited-state proton transfer and the ultimate decay of the
signal to relaxation through a twisted conical intersection. The total cost of
computing the observable signal (∼1700 graphics processing unit hours for
∼4 ns of electron dynamics) was markedly less than that of the ab
initio multiple spawning calculations used to compute the underlying
nonadiabatic dynamics.
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