arXiv subjects

Maxim F. Gelin

Publications and source records attributed to Maxim F. Gelin.

At least 19 recordsLinked to original sources

arXiv2026

An Ab initio Framework for Simulating Ultrafast Nonlinear Cavity Quantum Electrodynamics Spectra

In this letter we introduce a theoretical framework for the simulation of ultrafast transient absorption pump-probe spectra of molecular polaritons. We derive and implement the cavity quantum electrodynamics (QED) evolution equations of polaritonic states within the framework of the quasi-classical doorway-Window pproximation, hereto referred cQUEDA /sikeda/. This framework uses outputs from mixed quantum-classical dynamics simulations in the absence of the cavity. Then by including cavity parameters accounting for cavity rate loss, coupling strength, and frequency detuning, we simulate transient absorption pump-probe spectra. Consequently, we address one of the main standing problems of cavity QED, the simulation of polaritons ultrafast dynamics and nonlinear optical properties. We demonstrate the performance of our method by computing the ground-state bleach (GSB), stimulated emission (SE), and excited-state absorption (ESA) contributions of transient absorption pump-probe spectra of pyrazine strongly coupled to a cavity. The cQUEDA is an on-the-fly computationally efficient framework with low computer requirements: the pyrazine calculations, for example, took minutes on modern laptops. cQUEDA offers wide-ranging applicability and can be generalized to model diverse nonlinear spectroscopic signals and quantum optics responses.

physics.optics↗

arXiv2026

Ab Initio Simulation of Femtosecond Time-Resolved Multi-Pulse Spectroscopies applied to the Heptazine$\cdots$H$_2$O Complex

In multi-dimensional time-resolved spectroscopic experiments, multiple (more than two) short laser pulses with variable pulse delay times are employed for the time-resolved exploration of the photoinduced dynamics of molecular chromophores. In the present work, the quasi-classical doorway-window (DW) methodology recently developed for transient absorption pump-probe (PP) spectroscopy [M. F. Gelin et al., J. Chem. Theory Comput. 2021, 17, 2394] has been generalized to multi-pulse spectroscopies. Pump-push-probe (PPP) spectroscopy (involving three laser pulses) and pump-induced two-dimensional (P-2D) spectroscopy (involving five laser pulses) are considered as specific examples. The quasi-classical DW approximation results in conceptually simple and computationally efficient simulation protocols which are suitable for implementation with $ab$ $initio$ on-the-fly electronic-structure calculations. Simulations of PPP and P-2D spectra performed for the hydrogen-bonded heptazine$\cdots$H$_2$O complex illustrate that pump-stimulated experiments provide much richer information on the ultrafast radiationless relaxation dynamics of the excited electronic states of the heptazine$\cdots$H$_2$O complex than conventional PP and 2D experiments.

physics.chem-ph↗

arXiv2025

Simulation of Pump-Push Molecular Dynamics in the Heptazine-H2O Complex

Pump-push-probe spectroscopy was employed for the exploration of charge-separation processes in organic photovoltaic blends as well as for proton-coupled electron-transfer (PCET) reactions in hydrogen-bonded complexes of tri-anisole-heptazine with substituted phenols in organic solvents. In the present work, the electron and proton transfer dynamics driven by a femtosecond pump pulse and a time-delayed femtosecond push pulse has been studied with ab initio on-the-fly nonadiabatic trajectory calculations for the hydrogen-bonded heptazine-H2O complex. While the dynamics following the pump pulse is dominated by ultrafast radiationless energy relaxation to the long-lived lowest singlet excited state (S1) of the heptazine chromophore with only minor PCET reactivity, the re-excitation of the transient S1 population by the push pulse results in a much higher PCET reaction probability. These results illustrate that pump-push excitation has the potential to unravel the individual electron and proton transfer processes of PCET reactions on femtosecond time scales.

physics.chem-ph↗

arXiv2024

Imaging the Photochemistry of the Hydrogen-Bonded Heptazine-Water Complex with Femtosecond Time-Resolved Spectroscopy: A Computational Study

Graphitic carbon nitride ($g$-CN) has attracted vast interest as a promising inexpensive metal-free photocatalyst for water splitting with solar photons. The heptazine (Hz) molecule is the building block of graphitic carbon nitride. The photochemistry of the Hz molecule and derivatives thereof in protic environments has been the subject of several recent experimental and computational studies. In the present work, the hydrogen-bonded Hz$\cdots$H$_2$O complex was adopted as a model system for the exploration of photoinduced electron and proton transfer processes in this complex with quasi-classical nonadiabatic trajectory simulations, using the $ab$ $initio$ ADC(2) electronic-structure method and a computationally efficient surface-hopping algorithm. The population of the optically excited bright $^1ππ^*$ state of the Hz chromophore relaxes through three $^1nπ^*$ states and a low-lying charge-transfer state, which drives proton transfer from H$_2$O to Hz, to the long-lived optically dark S$_1$($ππ^*$) state of Hz. The imaging of this ultrafast and complex dynamics with femtosecond time-resolved transient absorption (TA) pump-probe (PP) spectroscopy and two-dimensional (2D) electronic spectroscopy (ES) was computationally explored in the framework of the quasi-classical doorway-window approximation. By comparison of the spectra of the Hz$\cdots$H$_2$O complex with those of the free Hz molecule, the effects of the hydrogen bond on the ultrafast internal conversion dynamics can be identified in the spectroscopic signals. Albeit the TA PP and 2D ES spectroscopies are primarily sensitive to electronic excited-state dynamics and less so to proton transfer dynamics, they nevertheless can provide mechanistic insights which can contribute to the acceleration of the optimization of photocatalysts for water splitting.

physics.chem-ph↗

arXiv2024

Tracking the Electron Density Changes in Excited States -- A Computational Study on Pyrazine

The development of X-ray free-electron lasers (XFELs) has enabled ultrafast X-ray diffraction (XRD) experiments, which are capable of resolving electronic/vibrational transitions and structural changes in molecules, or capturing molecular movies. While time-resolved XRD has received increasing attention, the extraction of information content from signals is challenging and requires theoretical support. In this work, we combined X-ray scattering theory and trajectory surface hopping approach to resolve dynamical changes in the electronic structure of photo-excited molecules by studying time evolution of electron density changes between electronic excited states and ground state. Using pyrazine molecule as an example, we show that key features of reaction pathways can be identified, enabling the capture of structural changes associated with electronic transitions for a photo-excited molecule.

physics.chem-ph↗

arXiv2024

On-the-Fly Simulation of Two-Dimensional Fluorescence-Excitation Spectra

Two-dimensional (2D) fluorescence-excitation (2D-FLEX) spectroscopy is a recently proposed nonlinear femtosecond technique for the detection of photoinduced dynamics. The method records a time-resolved fluorescence signal in its excitation- and detection-frequency dependence, and hence combines the exclusive detection of excited state dynamics (fluorescence) with signals resolved in both excitation and emission frequencies (2D electronic spectroscopy). In this work, we develop an on-the-fly protocol for the simulation of 2D-FLEX spectra of molecular systems, which is based on interfacing the classical doorway-window representation of spectroscopic responses with trajectory surface hopping simulations. Applying this methodology to the gas-phase pyrazine, we show that femtosecond 2D-FLEX spectra can deliver detailed information otherwise obtainable via attosecond spectroscopy.

physics.chem-ph↗

arXiv2024

Accelerating molecular vibrational spectra simulations with a physically informed deep learning model

In recent years, machine learning (ML) surrogate models have emerged as an indispensable tool to accelerate simulations of physical and chemical processes. However, there is still a lack of ML models that can accurately predict molecular vibrational spectra. Here, we present a highly efficient high-dimensional neural network potentials (HD-NNP) architecture to accurately calculate infrared (IR) and Raman spectra based on dipole moments and polarizabilities obtained on-the-fly via ML-molecular dynamics (MD) simulations. The methodology is applied to pyrazine, a prototypical polyatomic chromophore. The HD-NNP predicted energies are well within the chemical accuracy (1 kcal/mol), and the errors for HD-NNP predicted forces are only one-half of those obtained from a popular high-performance ML model. Compared to the ab initio reference, the HD-NNP predicted frequencies of IR and Raman spectra differ only by less than 8.3 cm^(-1), and the intensities of IR spectra and the depolarizaiton ratios of Raman spectra are well reproduced. The HD-NNP architecture developed in this work highlights importance of constructing highly accurate NNPs for predicting molecular vibrational spectra.

physics.chem-ph↗

arXiv2024

Finite temperature dynamics in a polarized sub-Ohmic heat bath: a hierarchical equations of motion-tensor train study

Dynamics of the sub-Ohmic spin-boson model under polarized initial conditions at finite temperature is investigated by employing both analytical tools and the numerically accurate hierarchical equations of motion-tensor train method. By analyzing the features of nonequilibrium dynamics, we discovered a bifurcation phenomenon which separates two regimes of the dynamics. It is found that before the bifurcation time, increasing temperature slows down the population dynamics, while the opposite effect occurs after the bifurcation time. The dynamics is highly sensitive to both initial preparation of the bath and thermal effects.

physics.chem-ph↗

arXiv2024

Finite-Temperature Hole-Magnon Dynamics in an Antiferromagnet

Employing the numerically accurate multiple Davydov Ansatz in combination with the thermo-field dynamics approach, we delve into interplay of the finite-temperature dynamics of holes and magnons in an antiferromagnet, which allows for scrutinizing previous predictions from self-consistent Born approximation while offering, for the first time, accurate finite-temperature computation of detailed magnon dynamics as a response and a facilitator to the hole motion. The study also uncovers pronounced temperature dependence of the magnon and hole populations, pointing to the feasibility of potential thermal manipulation and control of hole dynamics. Our methodology can be applied not only to the calculation of steady-state angular-resolved photoemission spectra, but also to the simulation of femtosecond terahertz pump-probe and other nonlinear signals for the characterization of antiferromagnetic materials.

cond-mat.str-el↗

arXiv2024

AI-enhanced on-the-fly simulation of nonlinear time-resolved spectra

Time-resolved spectroscopy is an important tool for unraveling the minute details of structural changes of molecules of biological and technological significance. The nonlinear femtosecond signals detected for such systems must be interpreted, but it is a challenging task for which theoretical simulations are often indispensable. Accurate simulations of transient-absorption or two-dimensional electronic spectra are, however, computationally very expensive, prohibiting the wider adoption of existing first-principles methods. Here, we report an AI-enhanced protocol to drastically reduce the computational cost of simulating nonlinear time-resolved electronic spectra which makes such simulations affordable for polyatomic molecules of increasing size. The protocol is based on doorway-window approach for the on-the-fly surface-hopping simulations. We show its applicability for the prototypical molecule of pyrazine for which it produces spectra with high precision with respect to ab initio reference while cutting the computational cost by at least 95% compared to pure first-principles simulations.

physics.chem-ph↗

arXiv2023

Dissipative Landau-Zener transitions in a three-level bow-tie model: accurate dynamics with the Davydov multi-D2 Ansatz

We investigate Landau-Zener (LZ) transitions in the three-level bow-tie model (3L-BTM) in a dissipative environment by using the numerically accurate method of multiple Davydov D2 Ansatze. We first consider the 3L-TBM coupled to a single harmonic mode, study evolutions of the transition probabilities for selected values of the model parameters, and interpret the obtained results with the aid of the energy diagram method. We then explore the 3L-TBM coupled to a boson bath. Our simulations demonstrate that sub-Ohmic, Ohmic and super-Ohmic boson baths have substantially different influences on the 3L-BTM dynamics, which cannot be grasped by the standard phenomenological Markovian single-rate descriptions. We also describe novel bath-induced phenomena which are absent in two-level LZ systems.

quant-ph↗

arXiv2023

Dynamics of dissipative Landau-Zener transitions in an anisotropic three-level system

We investigate the dynamics of Landau-Zener transitions in an anisotropic, dissipative three-level model (3-LZM) using the numerically accurate multiple Davydov D2 Ansatz in the framework of time-dependent variation. It is demonstrated that a non-monotonic relationship exists between the Landau-Zener transition probability and the phonon coupling strength when the 3-LZM is driven by a linear external field. Under the influence of a periodic driving field, phonon coupling may induce peaks in contour plots of the transition probability when the magnitude of the system anisotropy matches the phonon frequency. Dynamics of the 3-LZM have also been probed in the presence of a super-ohmic phonon bath when driven by a periodic driving field. It is found that both the period and the amplitude of the Rabi cycle decay exponentially with the increasing bath coupling strength.

quant-ph↗

arXiv2023

Exciton Dynamics and Time-Resolved Fluorescence in Nanocavity-Integrated Monolayers of Transition-Metal Dichalcogenides

We have developed an ab-initio-based fully-quantum numerically-accurate methodology for the simulation of the exciton dynamics and time- and frequency-resolved fluorescence spectra of the cavity-controlled two-dimensional materials at finite temperature and applied this methodology to the single-layer WSe2 system. This allowed us to establish dynamical and spectroscopic signatures of the polaronic and polaritonic effects as well as uncover their characteristic timescales in the relevant range of temperatures.

cond-mat.mes-hall↗

arXiv2022

Dynamics of the spin-boson model: the effect of bath initial conditions

Dynamics of the (sub-)Ohmic spin-boson model under various bath initial conditions is investigated by employing the Dirac-Frenkel time-dependent variational approach with the multiple Davydov $\mathrm{D_1}$ ansatz in the interaction picture. The validity of our approach is carefully checked by comparing results with those of the hierarchy equations of motion method. By analyzing the features of nonequilibrium dynamics, we identify the phase diagrams for different bath initial conditions. We find that for spectral exponent $s<s_c$, there exists a transition from coherent to quasicoherent dynamics with increasing the coupling strengths. For $s_c<s\leq{1}$, the coherent to incoherent crossover occurs at a certain coupling strength, and the quasicoherent dynamics emerges at much larger couplings. The initial preparation of the bath has considerable influence on the dynamics.

physics.chem-ph↗

arXiv2021

Ultrafast Internal Conversion Dynamics Through the on-the-fly Simulation of Transient Absorption Pump-Probe Spectra with Different Electronic Structure Methods

The ultrafast nonadiabatic internal conversion in azomethane is explored by the on-the-fly trajectory surface-hopping simulations of photoinduced dynamics and femtosecond transient absorption (TA) pump-probe (PP) spectra at three electronic-structure theory levels, OM2/MRCI, SA-CASSCF, and XMS-CASPT2. All these dynamics simulations predict ultrafast internal conversion. On the one hand, the OM2/MRCI and SA-CASSCF methods yield similar excited-state dynamics, while the XMS-CASPT2 method predicts a much slower population decay. On the other hand, the TA PP signals simulated at the SA-CASSCF and XMS-CASPT2 levels show the similar spectral features, particularly for the similar stimulated emission contributions, while the OM2/MRCI signals are quite different. This demonstrates that the nonadiabatic population dynamics and time-resolved stimulated emission signals may reflect different aspects of photoinduced processes. The combination of the dynamical and spectral simulations definitely provides more accurate and detailed information which sheds light on the microscopic mechanisms of photophysical and photochemical processes.

physics.chem-ph↗

arXiv2021

Effects of high pulse intensity and chirp in two-dimensional electronic spectroscopy of an atomic vapor

The effects of high pulse intensity and chirp on two-dimensional electronic spectroscopy signals are experimentally investigated in the highly non-perturbative regime using atomic rubidium vapor as clean model system. Data analysis is performed based on higher-order Feynman diagrams and non-perturbative numerical simulations of the system response. It is shown that higher-order contributions may lead to a fundamental change of the static appearance and beating-maps of the 2D spectra and that chirped pulses enhance or suppress distinct higher-order pathways. We further give an estimate of the threshold intensity beyond which the high-intensity effects become visible for the system under consideration.

physics.optics↗

arXiv2021

A model for dynamical solvent control of molecular junction electronic properties

Experimental measurements of electron transport properties of molecular junctions are often performed in solvents. Solvent-molecule coupling and physical properties of the solvent can be used as the external stimulus to control electric current through a molecule. In this paper, we propose a model, which includes dynamical effects of solvent-molecule interaction in the non-equilibrium Green's function calculations of electric current. The solvent is considered as a macroscopic dipole moment that reorients stochastically and interacts with the electrons tunnelling through the molecular junction. The Keldysh-Kadanoff-Baym equations for electronic Green's functions are solved in time-domain with subsequent averaging over random realisations of rotational variables using Furutsu-Novikov method for exact closure of infinite hierarchy of stochastic correlation functions. The developed theory requires the use of wide-band approximation as well as classical treatment of solvent degrees of freedom. The theory is applied to a model molecular junction. It is demonstrated that not only electrostatic interaction between molecular junction and solvent but also solvent viscosity can be used to control electrical properties of the junction. Aligning of the rotating dipole moment breaks particle-hole symmetry of the transmission favouring either hole or electron transport channels depending upon the aligning potential.

cond-mat.mes-hall↗

arXiv2021

First-passage time theory of activated rate chemical processes in electronic molecular junctions

Confined nanoscale spaces, electric fields and tunneling currents make the molecular electronic junction an experimental device for the discovery of new, out-of-equilibrium chemical reactions. Reaction-rate theory for current-activated chemical reactions is developed by combining a Keldysh nonequilibrium Green's functions treatment of electrons, Fokker-Planck description of the reaction coordinate, and Kramers' first-passage time calculations. The NEGF provide an adiabatic potential as well as a diffusion coefficient and temperature with local dependence on the reaction coordinate. Van Kampen's Fokker-Planck equation, which describes a Brownian particle moving in an external potential in an inhomogeneous medium with a position-dependent friction and diffusion coefficient, is used to obtain an analytic expression for the first-passage time. The theory is applied to several transport scenarios: a molecular junction with a single, reaction coordinate dependent molecular orbital, and a model diatomic molecular junction. We demonstrate the natural emergence of Landauer's blowtorch effect as a result of the interplay between the configuration dependent viscosity and diffusion coefficients. The resultant localized heating in conjunction with the bond-deformation due to current-induced forces are shown to be the determining factors when considering chemical reaction rates; each of which result from highly tunable parameters within the system.

cond-mat.mes-hall↗