arXiv subjects

Franco P. Bonafé

Publications and source records attributed to Franco P. Bonafé.

11 recordsLinked to original sources

arXiv2026

Linear and nonlinear vibrational excitation driven by molecular polaritons

Following our recent numerical study [arXiv:2601.16299 (2026)], we investigate vibrational excitation induced by transient optical driving in molecular ensembles strongly coupled to a cavity mode using the field-driven Holstein--Tavis--Cummings model. We analyze how pulsed excitation redistributes energy among electronic, photonic, and vibrational degrees of freedom in molecular polaritons. Vibrational dynamics are examined over a broad range of pulse durations and intensities within both the single-excitation approximation and a mean-field description of collective light--matter coupling. Despite their distinct formulations and microscopic descriptions, these two approaches yield consistent scaling relations for vibrational excitation. In particular, we disentangle linear and nonlinear contributions to vibrational excitation, which are reflected in distinct quadratic and quartic scaling behaviors with respect to the driving field amplitude (that is, linear and quadratic dependence on the incident pulse intensity). The microscopic origin of the nonlinear component is identified as a polariton-mediated intrapulse stimulated Raman-like process, enabled by a pulse spectral bandwidth large enough to overlap both upper and lower polaritons (rather than a conventional multi-pulse scheme). These results establish a unified framework for understanding vibrational excitation under pulsed polariton driving and provide guidance for the interpretation and control of ultrafast polariton experiments. Discrepancies between the mean-field and single-excitation approaches under certain pulsed conditions are identified and analyzed.

physics.chem-ph↗

arXiv2026

Collective Rabi-driven vibrational activation in molecular polaritons

Molecular polaritons arise from electronic or vibrational strong coupling (ESC and VSC) with confined electromagnetic fields. While these have been widely studied, the influence of electron-nuclear dynamics in driven cavities remains largely unknown. Here, we report a previously unrecognized mechanism of vibrational activation that emerges under collective ESC in driven optical cavities. Using simulations that self-consistently combine Maxwell's equations with quantum molecular dynamics, we show that collective electronic Rabi oscillations coherently drive nuclear motion. This effect is captured using both vibrational wave-packet dynamics in a minimal two-level model and atomistic simulations based on time-dependent density-functional tight-binding theory. Vibrational activation depends non-monotonically on the Rabi frequency and is maximized when the collective polaritonic splitting resonates with a molecular vibrational mode. The mechanism exhibits features consistent with a stimulated Raman-like relaxation mechanism. Our predictions are robust under realistic cavity conditions and provide the conditions in which they could be verified experimentally.

physics.comp-ph↗

arXiv2025

Molecular polariton dynamics in realistic cavities

The large number of degrees of freedom involved in polaritonic chemistry processes considerably restricts the systems that can be described by any ab initio approach, due to the resulting high computational cost. Semiclassical methods that treat light classically offer a promising route for overcoming these limitations. In this work, we present a new implementation that combines the numerical propagation of Maxwell's equations to simulate realistic cavities with quantum electron dynamics at the density functional tight-binding (DFTB) theory level. This implementation allows for the simulation of a large number of molecules described at the atomistic level, interacting with cavity modes obtained by numerically solving Maxwell's equations. By mimicking experimental setups, our approach enables the calculation of transmission spectra, in which we observe the corresponding polaritonic signals. In addition, we have access to local information, revealing complex responses of individual molecules that depend on the number, geometry, position, and orientation of the molecules inside the cavity.

physics.comp-ph↗

arXiv2025

Attosecond charge transfer in atomic-resolution scanning tunnelling microscopy

Electrons in atoms and molecules move on attosecond time scales. Deciphering their quantum dynamics in space and time calls for high-resolution microscopy at this speed. While scanning tunnelling microscopy (STM) driven with terahertz pulses has visualized sub-picosecond motion of single atoms, the advent of attosecond light pulses has provided access to the much faster electron dynamics. Yet, combining direct atomic spatial and attosecond temporal resolution remained challenging. Here, we reveal atomic-scale quantum motion of single electrons in attosecond lightwave-driven STM. Near-infrared single-cycle waveforms from phase-controlled optical pulse synthesis steer and clock electron tunnelling. By keeping the thermal load of the tip-sample junction stable, thereby eliminating thermal artifacts, we detect waveform-dependent currents on sub-cycle time scales. Our joint theory-experiment campaign shows that single-cycle near-infrared pulses can drive isolated electronic wave packets shorter than 1 fs. The angstrom-scale decay of the tunnelling current earmarks a fascinating interplay of multi-photon and field-driven dynamics. By balancing these effects, we sharply image a single copper adatom on a silver surface with lightwave-driven currents. This long-awaited fusion of attosecond science with atomic-scale STM makes elementary dynamics of electrons inside atoms, molecules and solids accessible to direct spatio-temporal videography and atom-scale petahertz electronics.

physics.optics↗

arXiv2025

High Harmonic Generation with Orbital Angular Momentum Beams: Beyond-dipole Corrections

We study the high harmonic generation with vortex beams beyond the dipole approximation. To do so we employ the full minimal coupling approach to account for multipolar coupling without truncation and describe the full spatio-temporal properties of the electromagnetic field. This allows us to investigate the beyond-dipole deviations in electron trajectories and the emitted power, where the influence of the orbital angular momentum contains both magnetic and quadrupolar effects. In contrast to the system driven by plane-wave light, we show that the non-linear dipole dynamics induced by the vortex beams are not confined to the polarization or propagation directions, but also have a component in the orthogonal direction. We identify the effects of the resulting symmetry breaking via increased beyond dipole corrections which are particularly apparent in even harmonics.

physics.atom-ph↗

arXiv2024

Full minimal coupling Maxwell-TDDFT: an ab initio framework for light-matter phenomena beyond the dipole approximation

We report the first ab initio, non-relativistic QED method that couples light and matter self-consistently beyond the electric dipole approximation and without multipolar truncations. This method is based on an extension of the Maxwell-Pauli-Kohn-Sham approach to a full minimal coupling Hamiltonian, where the space- and time-dependent vector potential is coupled to the matter system, and its back-reaction to the radiated fields is generated by the full current density. The implementation in the open-source Octopus code is designed for massively-parallel multiscale simulations considering different grid spacings for the Maxwell and matter subsystems. Here, we show the first applications of this framework to simulate renormalized Cherenkov radiation of an electronic wavepacket, magnetooptical effects with non-chiral light in non-chiral molecular systems, and renormalized plasmonic modes in a nanoplasmonic dimer. We show that in some cases the beyond-dipole effects can not be captured by a multipolar expansion Hamiltonian in the length gauge. Finally, we discuss further opportunities enabled by the framework in the field of twisted light and orbital angular momentum, inelastic light scattering and strong field physics.

cond-mat.mes-hall↗

arXiv2023

Tunable Tesla-scale magnetic attosecond pulses through ring-current gating

Coherent control over electron dynamics in atoms and molecules using high-intensity circularly-polarized laser pulses gives rise to current loops, resulting in the emission of magnetic fields. We propose and demonstrate with ab-initio calculations ``current-gating" schemes to generate direct or alternating-current magnetic pulses in the infrared spectral region, with highly tunable waveform and frequency, and showing femtosecond-to-attosecond pulse duration. In optimal conditions, the magnetic pulse can be highly isolated from the driving laser and exhibits a high flux density ($\sim1$ Tesla at few hundred nanometers from the source, with a pulse duration of 787 attoseconds) for application in forefront experiments of ultrafast spectroscopy. Our work paves the way toward the generation of attosecond magnetic fields to probe ultrafast magnetization, chiral responses, and spin dynamics.

physics.optics↗

arXiv2022

Dynamical evolution of the Schottky barrier as a determinant contribution to electron-hole pair stabilization and photocatalysis of plasmon-induced hot carriers

The harnessing of plasmon-induced hot carriers promises to open new avenues for the development of clean energies and chemical catalysis. The extraction of carriers before thermalization and recombination is of primordial importance to obtain appealing conversion yields. Here, hot carrier injection in the paradigmatic Au-TiO$_{2}$ system is studied by means of electronic and electron-ion dynamics. Our results show that pure electronic features (without considering many-body interactions or dissipation to the environment) contribute to the electron-hole separation stability. These results reveal the existence of a dynamic contribution to the interfacial potential barrier (Schottky barrier) that arises at the charge injection pace, impeding electronic back transfer. Furthermore, we show that this charge separation stabilization provides the time needed for the charge to leak to capping molecules placed over the TiO$_{2}$ surface triggering a coherent bond oscillation that will lead to a photocatalytic dissociation. We expect that our results will add new perspectives to the interpretation of the already detected long-lived hot carrier lifetimes, their catalytical effect, and concomitantly to their technological applications.

cond-mat.mes-hall↗

arXiv2022

Fano resonance and incoherent interlayer excitons in molecular van der Waals heterostructures

Complex van der Waals heterostructures from layered molecular stacks are promising optoelectronic materials offering means to efficient, modular charge separation and collection layers. The effect of stacking in the electrodynamics of such hybrid organic-inorganic two-dimensional materials remains largely unexplored, whereby molecular scale engineering could lead to advanced optical phenomena. For instance, tunable Fano engineering could make possible on-demand transparent conducting layers or photoactive elements, and passive cooling. We employ an adapted Gersten-Nitzan model and real time time-dependent density functional tight-binding to study the optoelectronics of self-assembled monolayers on graphene nanoribbons. We find Fano resonances that cause electromagnetic induced opacity and transparency, and reveal an additional incoherent process leading to interlayer exciton formation with a characteristic charge transfer rate. These results showcase hybrid van der Waals heterostructures as paradigmatic 2D optoelectronic stacks, featuring tunable Fano optics and unconventional charge transfer channels.

cond-mat.mes-hall↗

arXiv2020

A real-time time-dependent density functional tight-binding implementation for semiclassical excited state electron-nuclear dynamics and pump-probe spectroscopy simulations

The increasing need to simulate the dynamics of photoexcited molecular and nanosystems in the sub-picosecond regime demands new efficient tools able to describe the quantum nature of matter at a low computational cost. By combining the power of the approximate DFTB method with the semiclassical Ehrenfest method for nuclear-electron dynamics we have achieved a real-time time-dependent DFTB (TD-DFTB) implementation that fits such requirements. In addition to enabling the study of nuclear motion effects in photoinduced charge transfer processes, our code adds novel features to the realm of static and time-resolved computational spectroscopies. In particular, the optical properties of periodic materials such as graphene nanoribbons or the use of corrections such as the "LDA+U" and "pseudo SIC" methods to improve the optical properties in some systems, can now be handled at the TD-DFTB level. Moreover, the simulation of fully-atomistic time-resolved transient absorption spectra and impulsive vibrational spectra can now be achieved within reasonable computing time, owing to the good performance of the implementation and a parallel simulation protocol. Its application to the study of UV/visible light-induced vibrational coherences in molecules is demonstrated and opens a new door into the mechanisms of non-equilibrium ultrafast phenomena in countless materials with relevant applications.

physics.comp-ph↗

arXiv2016

Optical Properties of Graphene Nanoflakes: Shape Matters

In recent years there has been significant debate on whether the edge type of graphene nanoflakes (GNF) or graphene quantum dots (GQD) are relevant for their electronic structure, thermal stability and optical properties. Using computer simulations, we have proven that there is a fundamental difference in the calculated absorption spectra between samples of the same shape, similar size but different edge type, namely, armchair or zigzag edges. These can be explained by the presence of electronic structures near the Fermi level which are localized on the edges. These features are also evident from the dependence of band gap on the GNF size, which shows three very distinct trends for different shapes and edge geometries.

cond-mat.mes-hall↗