• LVC model
• MCTDH
• organic optoelectronics
• pentacene
• QM/QM′ embedding scheme
• simulation spectra

The field of organic optoelectronics is rapidly advancing, driven by technologies such
as organic photovoltaics (OPVs) and field-effect transistors (OFETs), which rely on
efficient light-to-charge conversion and current modulation in organic semiconduc-
tors. Among the most studied materials, pentacene stands out due to its high
crystallinity and exceptional charge mobility. However, simulating its optical
and excited-state dynamics remains challenging due to the interplay between local-
ized Frenkel excitons, intermolecular charge-transfer (CT) states, and vibrational
motions.
This thesis presents a bottom-up computational protocol to model the optical
properties and ultrafast excited-state dynamics of pentacene crystal. Central to
this approach is the construction of a Linear Vibronic Coupling (LVC) Hamiltonian
for large supercells, parametrized from high-level quantum chemical calculations on
smaller subsystems.
The protocol begins with simulating the vibronic spectrum of a pentacene monomer
to identify key intramolecular vibrational modes and their electron-phonon coupling
strengths. A diabatization technique is then applied to dimer and trimer fragments
to extract energies and couplings of localized (Frenkel) exciton and charge trans-
fer (CT) states. These parameters are integrated into a Hamiltonian capable of
describing extended crystal supercells. The model successfully reproduces experi-
mental linear absorption spectra, capturing Davydov splitting and J-/H-aggregate
features. The results highlight the importance of Frenkel–CT mixing in determining
the optical response. Ultrafast dynamics simulations, performed via the Multi-
Configuration Time-Dependent Hartree (MCTDH) method, reveal complex popu-
lation transfer among excitonic states following photoexcitation. The impact of the
crystalline environment is further tested through a QM/QM′ embedding scheme.
This thesis establishes a multiscale methodology for predicting and interpreting
the photophysics of organic crystals, contributing to the rational design of next-
generation optoelectronic materials.