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We present a new software module, QRCODE (Quantum Research for Calculating Optically Driven Excitations), for massively parallelized real-time time-dependent density functional theory (RT-TDDFT) calculations of periodic systems in the open-source Qbox software package. Our approach utilizes a custom implementation of a fast Fourier transformation scheme that significantly reduces inter-node message passing interface (MPI) communication of the major computational kernel and shows impressive scaling up to 16,344 CPU cores. In addition to improving computational performance, QRCODE contains a suite of various time propagators for accurate RT-TDDFT calculations. As benchmark applications of QRCODE, we calculate the current density and optical absorption spectra of hexagonal boron nitride (h-BN) and photo-driven reaction dynamics of the ozone-oxygen reaction. We also calculate the second and higher harmonic generation of monolayer and multi-layer boron nitride structures as examples of large material systems. Our optimized implementation of RT-TDDFT in QRCODE enables large-scale calculations of real-time electron dynamics of chemical and material systems with enhanced computational performance and impressive scaling across several thousand CPU cores.

Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light‐induced proton reduction systems. Developing competitive base metal dyads is mandatory for a more sustainable future. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored. A Fe─Co dyad that exhibits photocatalytic H2 production activity is studied using femtosecond X‐ray emission spectroscopy, complemented by ultrafast optical spectroscopy and theoretical time‐dependent DFT calculations, to understand the electronic and structural dynamics after photoexcitation and during the subsequent charge transfer process from the FeII photosensitizer to the cobaloxime catalyst. This novel approach enables the simultaneous measurement of the transient X‐ray emission at the iron and cobalt K‐edges in a two‐color experiment. With this methodology, the excited state dynamics are correlated to the electron transfer processes, and evidence of the Fe→Co electron transfer as an initial step of proton reduction activity is unraveled. [ABSTRACT FROM AUTHOR]

In recent decades, the de Broglie-Bohm or 'pilot wave' interpretation of quantum mechanics–especially its concept of the 'quantum trajectory'–has inspired a plethora of computational methods in molecular and chemical physics. One particularly promising subclass of such methods are the 'interacting quantum trajectory' (IQT) methods, for which an ensemble of trajectories is propagated independently of–and without any recourse to–an underlying wavefunction. In this work, an IQT version of the Pauli equation is developed–enabling spin to be incorporated into IQT theories for the first time, to the authors' knowledge. The new trajectory-based dynamical equations are then used to solve two iconic quantum problems involving spin: the 'quantum spin flipper', and the Stern-Gerlach experiment. [ABSTRACT FROM AUTHOR]

Chorus waves are intense electromagnetic emissions critical in modulating electron dynamics. In this study, we perform two‐dimensional particle‐in‐cell simulations to investigate self‐consistent wave‐particle interactions with oblique chorus waves. We first analyze the electron dynamics sampled from cyclotron and Landau resonances with waves, and then quantify the advection and diffusion coefficients through statistical studies. It is found that phase‐trapped cyclotron resonant electrons satisfy the second‐order resonance condition and gain energy from waves. While phase‐bunched cyclotron resonant electrons cannot remain in resonance for long periods. They transfer energy to waves and are scattered to smaller pitch angles. Landau resonant electrons are primarily energized by waves. For both types of resonances, advection coefficients are greater than diffusion coefficients when the wave amplitude is large. Our study highlights the important role of advection in electron dynamics modulation resulting from nonlinear wave‐particle interactions. Plain Language Summary: Wave‐particle interactions can modulate electron distributions through advection and diffusion. Previous studies focusing on advection and diffusion primarily relied on test particle simulations, which uses a simplified model of wave evolution. In this study, we perform self‐consistent simulations to investigate the wave‐particle interactions with chorus waves and quantify the advection and diffusion coefficients of resonant electrons. It is found that advection coefficients are greater than diffusion coefficients in both cyclotron and Landau resonances, indicating the significant role of nonlinear wave‐particle interactions. The quantification of advection and diffusion coefficients in a self‐consistent system is important for understanding and predicting the loss and energization processes in radiation belt electrons. This study complements previous diffusion models that regarded the evolution of electron dynamics in wave‐particle interactions as a slow diffusive process. Key Points: Electron advection and diffusion in wave‐particle interactions with chorus waves are investigated through self‐consistent simulationsThe second‐order time derivative of gyrophase angle is nearly zero for phase‐trapped electrons but is negative for phase‐bunched electronsThe advection and diffusion coefficients for cyclotron and Landau resonant electrons interacting with chorus waves are quantified [ABSTRACT FROM AUTHOR]

Abstract Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light‐induced proton reduction systems. Developing competitive base metal dyads is mandatory for a more sustainable future. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored. A Fe─Co dyad that exhibits photocatalytic H2 production activity is studied using femtosecond X‐ray emission spectroscopy, complemented by ultrafast optical spectroscopy and theoretical time‐dependent DFT calculations, to understand the electronic and structural dynamics after photoexcitation and during the subsequent charge transfer process from the FeII photosensitizer to the cobaloxime catalyst. This novel approach enables the simultaneous measurement of the transient X‐ray emission at the iron and cobalt K‐edges in a two‐color experiment. With this methodology, the excited state dynamics are correlated to the electron transfer processes, and evidence of the Fe→Co electron transfer as an initial step of proton reduction activity is unraveled.

We present a new implementation of real-time time-dependent density functional theory (RT-TDDFT) for calculating excited-state dynamics of periodic systems in the open-source Python-based PySCF software package. Our implementation uses Gaussian basis functions in a velocity gauge formalism and can be applied to periodic surfaces, condensed-phase, and molecular systems. As representative benchmark applications, we present optical absorption calculations of various molecular and bulk systems and a real-time simulation of field-induced dynamics of a (ZnO)4 molecular cluster on a periodic graphene sheet. We present representative calculations on optical response of solids to infinitesimal external fields as well as real-time charge-transfer dynamics induced by strong pulsed laser fields. Due to the widespread use of the Python language, our RT-TDDFT implementation can be easily modified and provides a new capability in the PySCF code for real-time excited-state calculations of chemical and material systems.

Chorus subpackets are the wave packets with modulated amplitudes in chorus waves, commonly observed in the magnetospheres of Earth and other planets. Nonlinear wave‐particle interactions have been suggested to play an important role in subpacket formation, yet the corresponding electron dynamics remain not fully understood. In this study, we have investigated the electron trapping through cyclotron resonance with subpackets, using a self‐consistent general curvilinear plasma simulation code simulation model in dipole fields. The electron trapping period has been quantified separately through electron dynamic analysis and theoretical derivation. Both methods indicate that the electron trapping period is shorter than the subpacket period/duration. We have further established the relation between electron trapping period and subpacket period through statistical analysis using simulation and observational data. Our study demonstrates that the nonlinear electron trapping through cyclotron resonance is the dominant mechanism responsible for subpacket formation. Plain Language Summary: The spectrum of chorus waves comprises a series of subpackets, characterized by modulated amplitudes within a timescale of ∼10–100 milliseconds. In this study, we have investigated the self‐consistent wave‐particle interactions with subpackets, using two‐dimensional particle‐in‐cell simulations in dipole fields. Cyclotron resonant electrons are trapped in wave phases, and we have measured their trapping period. Since these electrons move in the opposite direction of subpacket propagation, the corresponding trapping period is smaller than the period of subpackets. We have further established the relation between the two periods and validated it through both simulation and observational data. This relation facilitates evaluating electron trapping period from direct measurement of subpackets in observations. Our study sheds important lights on the key role of nonlinear electron trapping through cyclotron resonance in the formation of subpackets. Key Points: Electron trapping dynamics in the formation of quasi‐parallel chorus subpackets have been investigatedThe linkage between electron trapping period and subpacket period is quantified via a geometric relation, where the trapping period is shorterThe proposed relation between electron trapping period and subpacket period is an extension of the classical results of O'Neil (1965) [ABSTRACT FROM AUTHOR]

We have simulated two mechanisms, direct and superexchange, for the electron transfer in a model Bis(hydrazine) Radical Cation, which consists of two hydrazine moieties coupled by a benzene ring. The computations, that are inspired by the attochemistry approach, focus on the electron dynamics arising from a coherent superposition of four cationic states. The electron dynamics, originating from a solution of the time dependent Schrödinger equation within the Ehrenfest method, is coupled to the relaxation of the nuclei. Both direct (ca. 15 fs dynamics) and superexchange (ca. 2 fs dynamics) mechanisms are observed and turn out to lie on a continuum depending on the strength of the coupling of the benzene bridge electron dynamics with the hydrazine chromophore dynamics. This contrasts with the chemical pathway approach where the direct mechanism is completely non-adiabatic via a conical intersection, while the superexchange mechanism involves an intermediate radical with the unpaired electron localized on the benzene ring. Thus, with the attochemistry-inspired electron dynamics approach, one can distinguish direct from superexchange mechanisms depending on the strength of the coupling of two types of electron dynamics: the slow hydrazine dynamics (ca. 15 fs) and the fast benzene linker dynamics (ca. 2 fs). In this model bis(hydrazine) radical cation, only when the intermediate coupler is in an anti-quinoid state, does one see the coupling of the bridge and hydrazine chromophore dynamics. [ABSTRACT FROM AUTHOR]

Abstract Chorus waves are intense electromagnetic emissions critical in modulating electron dynamics. In this study, we perform two‐dimensional particle‐in‐cell simulations to investigate self‐consistent wave‐particle interactions with oblique chorus waves. We first analyze the electron dynamics sampled from cyclotron and Landau resonances with waves, and then quantify the advection and diffusion coefficients through statistical studies. It is found that phase‐trapped cyclotron resonant electrons satisfy the second‐order resonance condition and gain energy from waves. While phase‐bunched cyclotron resonant electrons cannot remain in resonance for long periods. They transfer energy to waves and are scattered to smaller pitch angles. Landau resonant electrons are primarily energized by waves. For both types of resonances, advection coefficients are greater than diffusion coefficients when the wave amplitude is large. Our study highlights the important role of advection in electron dynamics modulation resulting from nonlinear wave‐particle interactions.

Since the invention of laser, a huge number of new technological advancements have happened, along with the generation of new basic science knowledge, which has paved the way to study and control matter on femtosecond and attosecond time scales. Since 2001, ultrafast science has ushered into the attosecond era, with the generation, characterization, and applications of coherent attosecond pulses of light. Experimental methods to generate attosecond pulses of light to study electron dynamics in matter have been awarded the Nobel Prize in Physics 2023. In this article, we provide a pedagogical overview of the physics and technology behind attosecond pulses and their applications in exploring the dynamics of matter on an ever-shorter time scale. We begin with milestones that led to the attosecond era and explain the basic mechanism behind the generation and characterization of attosecond pulses. We describe the experimental implementation of the attosecond setup and discuss some applications in resolving the attosecond phenomenon. Emerging directions in this new field are also mentioned. [ABSTRACT FROM AUTHOR]

A pair of simulated left and right circularly polarized ultra‐fast laser pulses of duration 20 femtoseconds that induce a mixture of excited states are applied to ethane. The response of the electron dynamics is investigated within the next generation quantum theory of atoms in molecules (NG‐QTAIM) using third‐generation eigenvector‐trajectories which are introduced in this work. This enables an analysis of the mechanical and chiral properties of the electron dynamics of ethane without needing to subject the C‐C bond to external torsions as was the case for second‐generation eigenvector‐trajectories. The mechanical properties, in particular, the bond‐flexing and bond‐torsion were found to increase depending on the plane of the applied laser pulses. The bond‐flexing and bond‐torsion, depending on the plane of polarization, increases or decreases after the laser pulses are switched off. This is explainable in terms of directionally‐dependent effects of the long‐lasting superpositions of excited states. The chiral properties correspond to the ethane molecule being classified as formally achiral consistent with previous NG‐QTAIM investigations. Future planned investigations using ultra‐fast circularly polarized lasers are briefly discussed. [ABSTRACT FROM AUTHOR]

Ultrafast electron dynamics have made rapid progress in the last few years. With Jellyfish, we now introduce a program suite that enables to perform the entire workflow of an electron‐dynamics simulation. The modular program architecture offers a flexible combination of different propagators, Hamiltonians, basis sets, and more. Jellyfish can be operated by a graphical user interface, which makes it easy to get started for nonspecialist users and gives experienced users a clear overview of the entire functionality. The temporal evolution of a wave function can currently be executed in the time‐dependent configuration interaction method (TDCI) formalism, however, a plugin system facilitates the expansion to other methods and tools without requiring in‐depth knowledge of the program. Currently developed plugins allow to include results from conventional electronic structure calculations as well as the usage and extension of quantum‐compute algorithms for electron dynamics. We present the capabilities of Jellyfish on three examples to showcase the simulation and analysis of light‐driven correlated electron dynamics. The implemented visualization of various densities enables an efficient and detailed analysis for the long‐standing quest of the electron–hole pair formation. This article is categorized under:Theoretical and Physical Chemistry > SpectroscopySoftware > Simulation Methods [ABSTRACT FROM AUTHOR]

Abstract Chorus subpackets are the wave packets with modulated amplitudes in chorus waves, commonly observed in the magnetospheres of Earth and other planets. Nonlinear wave‐particle interactions have been suggested to play an important role in subpacket formation, yet the corresponding electron dynamics remain not fully understood. In this study, we have investigated the electron trapping through cyclotron resonance with subpackets, using a self‐consistent general curvilinear plasma simulation code simulation model in dipole fields. The electron trapping period has been quantified separately through electron dynamic analysis and theoretical derivation. Both methods indicate that the electron trapping period is shorter than the subpacket period/duration. We have further established the relation between electron trapping period and subpacket period through statistical analysis using simulation and observational data. Our study demonstrates that the nonlinear electron trapping through cyclotron resonance is the dominant mechanism responsible for subpacket formation.

The lattice of the fourth-generation of the SYLA electron storage synchrotron of 6 GeV is scaled using the resources of the National Research Center Kurchatov Institute. Parameters of the storage synchrotron that provide design parameters of electron beams in the accumulator have been calculated. The dynamic aperture, momentum acceptance, and Touschek lifetime of the beams were determined, both in the case of no errors in the adjustment of magnetic structure elements and field values in a closed orbit and in their presence, taking into account losses due to synchrotron radiation and quantum excitation. Kicker magnets have been adapted to provide efficient off-axis injection. [ABSTRACT FROM AUTHOR]

We have investigated the interaction of intense laser pulses with silicon film using the one-dimensional Three-Temperature Model previously presented by Venkat and Otobe (Applied Physics Express, 15(4), 041008 (2022)). Our study focuses on how the excitation process in thin films, ranging from tens of nanometers to a few microns, is affected by the interference of the laser field at a wavelength of 775 nm. Our findings show that when the thickness of the film is less than 1.5 µm, the damage thresholds exhibit oscillations due to the interference of the laser field over a period of 100 nm, which is equivalent to half the wavelength in silicon. We also observe that the thermal damage threshold of the rear surface and inside film is lower than that of the front surface when the thickness is less than 0.3 µm and 0.5 µm, respectively. These results emphasize the significance of the size effect in the laser processing of silicon and have important implications for the optimization of the laser processing techniques of silicon. [ABSTRACT FROM AUTHOR]

There is still a lack of understanding of a possible mechanical ablation mechanism and the causes of thermal degradation of thin indium tin oxide (ITO) films. A dual hyperbolic two temperature model is applied to the ultrashort pulsed laser ablation process of 100 nm indium tin oxide films. The model describes transient optical properties by taking into account the changes in the complex dielectric function due to laser excitation. The laser excitation is modelled by free electron dynamics and a nonlinear absorption coefficient for a laser pulse duration of 700 fs and a central wavelength of 1056 nm. For peak fluences F ≤ 0:35 J/cm², we find that the modeled strain exceeds the yield strain in the regions where the experimental craters show signs of mechanical ablation behavior. For larger peak fluences F > 0:35 J/cm² the model predicts lattice temperatures Tl exceeding the melting temperature Tmelt; ITO of indium tin oxide. The computed depth where Tl ≤ Tmelt;ITO agrees with the measured ablation crater depths. [ABSTRACT FROM AUTHOR]

We investigate the electron dynamics and generation of whistler‐mode waves inside a short large‐amplitude magnetic structure (SLAMS) based on Magnetospheric Multiscale Satellite observations and test particle simulations. The buildup of energetic reflected ions caused by the SLAMS's intense magnetic fields favors the resonance condition of solar wind ions of ion‐ion non‐resonant mode. This might further steepen the SLAMS, leading to the Betatron acceleration of electrons and generating the whistler‐mode waves locally ahead of the peak of the magnetic field. In regions behind the peaked magnetic field, electrons are decelerated by the convection electric field during gradient drift and the whistler‐mode waves are rapidly decayed. Our study provides new insights into electron acceleration and the generation of whistler‐mode waves near the quasi‐parallel shock. Plain Language Summary: On the quasi‐parallel side of the bow shock, ultra‐low frequency waves and nonlinear structures such as shocklet and short large‐amplitude magnetic structure (SLAMS) are commonly observed, which are powered by energetic reflected ions and form in different stages during steepening. Solar wind ions are heated significantly inside these nonlinear structures. However, what role electrons played inside these structures is full of mystery. Recent numerical simulations reveal that electron dynamics and whistler‐mode waves inside these structures are responsible for triggering bow shock reconnection on the quasi‐parallel side. In this paper, we focus on electron distributions and acceleration inside SLAMS. Electrons are accelerated/decelerated in regions prior to/after the peaked magnetic field, exciting/decaying whistler‐mode waves locally which well‐regulated the electron distribution. Our work reveals the electron dynamics inside the SLAMS and provides new insights into plasma heating and acceleration near the quasi‐parallel shock. Key Points: Whistler‐mode waves are locally generated through the first‐order resonance of the electrons inside the short large‐amplitude magnetic structure (SLAMS)SLAMS steepening primarily impacts electron acceleration and whistler‐mode wave generationElectron deceleration by the v × B electric field during gradient drift leads to whistler‐mode wave decay at the trailing edge of SLAMS [ABSTRACT FROM AUTHOR]

With high‐resolution data from Magnetospheric Multiscale (MMS) mission, an ion‐scale flux rope (FR) with a heavily tilted axis is observed in the tailward outflow of a magnetic reconnection in the terrestrial magnetotail. Combined with the field‐aligned electron distribution and positions of MMS when the X‐line and FR are observed, the tilted axis is inferred to be caused by the extension of the X‐line in the dawn‐dusk direction. J · E′ is negative and electrons are losing energy in the FR. An ion‐scale electron vortex embedded in the plane perpendicular to the axis is observed inside FR. The induced magnetic field generated by the electron vortex has the same direction as the axial component, which can contribute to the axial component and increase the magnetic flux of the FR. Such electron vortex FRs may be an essential carrier of magnetic flux from near‐Earth X‐line to distant X‐line or interplanetary space. Plain Language Summary: Magnetic reconnection is an efficient energy and magnetic flux release process in the magnetotail. It is well known that dipolarization front is an important carrier of magnetic flux to Earth. However, how the magnetic flux transports at the tailward side is rarely concerned. In this work, we present an observation of an electron vortex flux rope as a new possible candidate. The embedded electron vortex generates an induced magnetic field with the same direction as the axial component of the flux rope, which is self‐consistent and can contribute to the enhancement of the magnetic flux carried by the flux rope by converting energy from electrons to the magnetic field. Our observations can contribute to understand the dynamics of the magnetotail. Key Points: An ion‐scale flux rope with an electron vortex embedded is observed in the tailward outflow of a magnetic reconnection eventThe tilted axis of the flux rope is due to the extension of the X‐line in the dawn‐dusk directionThe electron vortex flux rope may be an essential carrier of magnetic flux to distant tail or interplanetary space [ABSTRACT FROM AUTHOR]

We reviewed the time-dependent multiconfiguration self-consistent-field (TD-MCSCF) method and the time-dependent optimized coupled-cluster (TD-OCC) method for first-principles simulations of high-field phenomena such as tunneling ionization and high-order harmonic generation in atoms and molecules irradiated by a strong laser field. These methods provide a flexible and systematically improvable description of the multielectron dynamics by expressing the all-electron wavefunction by configuration interaction expansion or coupled-cluster expansion, using time-dependent one-electron orbital functions. The time-dependent variational principle plays a key role in deriving these methods while satisfying gauge invariance and Ehrenfest theorem. The real-time/real-space implementation with an absorbing boundary condition enables the simulation of high-field processes involving multiple excitation and ionization. We present a detailed, comprehensive discussion of such features of the TD-MCSCF and TD-OCC methods. [ABSTRACT FROM AUTHOR]

The dramatic progress of experimental attosecond science has called for the development of new theoretical and computational tools capable of accurately model the correlated electron dynamics triggered by attosecond molecular photoionization. We describe the nature and the main outcome of this development, with particular focus on the B‐spline ADC and RCS‐ADC ab initio methods. This article is categorized under:Electronic Structure Theory > Ab Initio Electronic Structure MethodsSoftware > Simulation MethodsTheoretical and Physical Chemistry > Spectroscopy [ABSTRACT FROM AUTHOR]

In the past three decades, first principles-based fully kinetic particle-in-cell Monte Carlo collision (PIC/MCC) simulations have been proven to be an important tool for the understanding of the physics of low pressure capacitive discharges. However, there is a long-standing issue that the plasma density determined by PIC/MCC simulations shows quantitative deviations from experimental measurements, even in argon discharges, indicating that certain physics may be missing in previous modeling of the low pressure radio frequency (rf) driven capacitive discharges. In this work, we report that the energetic electron-induced secondary electron emission (SEE) and excited state atoms play an important role in low pressure rf capacitive argon plasma discharges. The ion-induced secondary electrons are accelerated by the high sheath field to strike the opposite electrode and produce a considerable number of secondary electrons that lead to additional ionizing impacts and further increase of the plasma density. Importantly, the presence of excited state species even further enhances the plasma density via excited state neutral and resonant state photon-induced SEE on the electrode surface. The PIC/MCC simulation results show good agreement with the recent experimental measurements in the low pressure range (1–10 Pa) that is commonly used for etching in the semiconductor industry. At the highest pressure (20 Pa) and driving voltage amplitudes 250 and 350 V explored here, the plasma densities from PIC/MCC simulations considering excited state neutrals and resonant photon-induced SEE are quantitatively higher than observed in the experiments, requiring further investigation on high pressure discharges. [ABSTRACT FROM AUTHOR]

Nonlinear dynamics in quantum theory is an old area which has received considerable recent impetus. In particular, the possibility and detection of chaos in the quantum realm is a topic with far-reaching consequences. The time-independent features of quantum systems with classically chaotic counterparts had been explored before by a number of workers. However, dynamical signatures of chaos in quantum systems independent of classically chaotic counterparts is still a relatively new area of research. This article recounts our research in that direction which yielded (1) a new dynamical signature of quantum chaos; (2) a methodology to discuss chaos even for systems where classical analogues do not exist; and (3) a connection between the dynamics of atomic and molecular systems under strong external forces and dynamical quantum chaos. These aspects are briefly described here. [ABSTRACT FROM AUTHOR]

Abstract With high‐resolution data from Magnetospheric Multiscale (MMS) mission, an ion‐scale flux rope (FR) with a heavily tilted axis is observed in the tailward outflow of a magnetic reconnection in the terrestrial magnetotail. Combined with the field‐aligned electron distribution and positions of MMS when the X‐line and FR are observed, the tilted axis is inferred to be caused by the extension of the X‐line in the dawn‐dusk direction. J · E′ is negative and electrons are losing energy in the FR. An ion‐scale electron vortex embedded in the plane perpendicular to the axis is observed inside FR. The induced magnetic field generated by the electron vortex has the same direction as the axial component, which can contribute to the axial component and increase the magnetic flux of the FR. Such electron vortex FRs may be an essential carrier of magnetic flux from near‐Earth X‐line to distant X‐line or interplanetary space.

We train a model atom to recognize pixel-drawn digits based on hand-written numbers in the range 0–9, employing intense light–matter interaction as a computational resource. For training, the images of the digits are converted into shaped laser pulses (data input pulses). Simultaneously with an input pulse, another shaped pulse (program pulse), polarized in the orthogonal direction, is applied to the atom and the system evolves quantum mechanically according to the time-dependent Schrödinger equation. The purpose of the optimal program pulse is to direct the system into specific atomic final states (classification states) that correspond to the input digits. A success rate of about 40% is achieved when using a basic optimization scheme that might be limited by the computational resources for finding the optimal program pulse in a high-dimensional search space. Our key result is the demonstration that the laser-programmed atom is able to generalize, i.e. successful classification is not limited to the training examples, but also the classification of previously unseen images is improved by training. This atom-sized machine-learning image-recognition scheme operates on time scales down to tens of femtoseconds, is scalable towards larger (e.g. molecular) systems, and is readily reprogrammable towards other learning/classification tasks. An experimental implementation of the scheme using ultrafast polarization pulse shaping and differential photoelectron detection is within reach.

We perform an ab initio non-adiabatic molecular dynamics simulation to investigate the non-equilibrium spin and electron dynamics in a prototypical topological insulator (TI) Bi2Se3. Different from the ground state, we reveal that backscattering can happen in an oscillating manner between time-reversal pair topological surface states (TSSs) in the non-equilibrium dynamics. Analysis shows the phonon excitation induces orbital composition change by electron-phonon interaction, which further stimulates spin canting through spin-orbit coupling. The spin canting of time-reversal pair TSSs leads to the non-zero non-adiabatic coupling between them and then issues in backscattering. Both the spin canting and backscattering result in ultrafast spin relaxation with a timescale around 100 fs. This study provides critical insights into the non-equilibrium electron and spin dynamics in TI at the ab initio level and paves a way for the design of ultrafast spintronic materials.

With the three-dimensional semi-classical ensemble model, we studied the non-sequential double ionization by orthogonal two-color laser pulses. Our calculations show that the proportion of events experiencing multiple returnings, the sum of the final energies of two electrons, and the ion momentum distribution depend on the relative phase of the two-color fields, exhibiting oscillatory behavior with a period of π. Back analysis of these trajectories reveals that we can control the recollision energy of the electron by changing the relative phase of the two-color laser pulse. As a consequence, the trajectories of multiple-returning ions change with the relative phase, resulting in relative-phase-dependent ion momentum distributions. The result shows that the momentum distribution of the ions in the trajectories of multiple returnings is clearly wider than that for the case of single returning. For the multiple-returning events, the binary recollision leads to a smaller scattering angle of the first electron.

Quantum chaos is reviewed from the viewpoint of "what is molecule?", particularly placing emphasis on their dynamics. Molecules are composed of heavy nuclei and light electrons, and thereby the very basic molecular theory due to Born and Oppenheimer gives a view that quantum electronic states provide potential functions working on nuclei, which in turn are often treated classically or semiclassically. Therefore, the classic study of chaos in molecular science began with those nuclear dynamics particularly about the vibrational energy randomization within a molecule. Statistical laws in probabilities and rates of chemical reactions even for small molecules of several atoms are among the chemical phenomena requiring the notion of chaos. Particularly the dynamics behind unimolecular decomposition are referred to as Intra-molecular Vibrational energy Redistribution (IVR). Semiclassical mechanics is also one of the main research fields of quantum chaos. We herein demonstrate chaos that appears only in semiclassical and full quantum dynamics. A fundamental phenomenon possibly giving birth to quantum chaos is "bifurcation and merging" of quantum wavepackets, rather than "stretching and folding" of the baker's transformation and the horseshoe map as a geometrical foundation of classical chaos. Such wavepacket bifurcation and merging are indeed experimentally measurable as we showed before in the series of studies on real-time probing of nonadiabatic chemical reactions. After tracking these aspects of molecular chaos, we will explore quantum chaos found in nonadiabatic electron wavepacket dynamics, which emerges in the realm far beyond the Born-Oppenheimer paradigm. In this class of chaos, we propose a notion of Intra-molecular Nonadiabatic Electronic Energy Redistribution (INEER), which is a consequence of the chaotic fluxes of electrons and energy within a molecule. [ABSTRACT FROM AUTHOR]

A detailed analysis of the electronic structure and decay dynamics in a symmetric system with three electrons in three linearly aligned binding sites representing quantum dots (QDs) is given. The two outer A QDs are two-level potentials and can act as (virtual) photon emitters, whereas the central B QD can be ionized from its one level into a continuum confined on the QD axis upon absorbing virtual photons in the inter-Coulombic decay (ICD) process. Two scenarios in such an A B A array are explored. One ICD process is from a singly excited resonance state, whose decay releasing one virtual photon we find superimposed with resonance energy transfer among both A QDs. Moreover, the decay-process manifold for a doubly excited (DE) resonance is explored, in which collective ICD among all three sites and excited ICD among the outer QDs engage. Rates for all processes are found to be extremely low, although ICD rates with two neighbors are predicted to double compared to ICD among two sites only. The slowing is caused by Coulomb barriers imposed from ground or excited state electrons in the A sites. Outliers occur on the one hand at short distances, where the charge transfer among QDs mixes the possible decay pathways. On the other hand, we discovered a shape resonance-enhanced DE-ICD pathway, in which an excited and localized B * shape resonance state forms, which is able to decay quickly into the final ICD continuum. [ABSTRACT FROM AUTHOR]

We consider the problem of learning density-dependent molecular Hamiltonian matrices from time series of electron density matrices, all in the context of Hartree– Fock theory. Prior work developed a solution to this problem for small molecular systems with density and Hamiltonian matrices of size at most 6 × 6. Here, using a battery of techniques, we scale prior methods to larger molecular systems with, for example, 29 × 29 matrices. This includes systems that either have more electrons or are expressed in large basis sets such as 6-311++G**. Scaling the method to larger systems enhances its relevance for realistic applications in chemistry and physics. To achieve this scaling, we apply dimensionality reduction, ridge regression and analytic computation of Hessians. Through the combination of these techniques, we are able to learn Hamiltonians by minimizing an objective function that encodes local propagation error. Importantly, these learned Hamiltonians can then be used to predict electron dynamics for thousands of steps: When we use our learned Hamiltonians to numerically solve the time-dependent Hartree–Fock equation, we obtain predicted dynamics that are in close quantitative agreement with ground truth dynamics. This includes field-off trajectories similar to the training data and field-on trajectories outside of the training data. [ABSTRACT FROM AUTHOR]

Increasing the efficiency of visible-light-driven water splitting systems will require improvements in the charge separation characteristics and redox reaction kinetics associated with narrow-bandgap photocatalysts. Although the traditional approach of loading a single cocatalyst on selective facets provides reaction sites and reduces the reaction overpotential, pronounced surface charge carrier recombination still results in limited efficiency increases. The present study demonstrates a significant improvement in the hydrogen evolution activity of the layered single-crystal photocatalyst Y 2 Ti 2 O 5 S 2 . Increased performance is obtained through sequential loading of Pt cocatalysts using a two-step process followed by photodeposition of Cr 2 O 3 nanolayers. The stepwise deposition of Pt involved an impregnation-reduction pretreatment with subsequent photodeposition and produced numerous hydrogen production sites while promoting electron capture. The Cr 2 O 3 shells formed on Pt nanoparticles further promoted electron transfer from the Pt to the water and inhibited surface carrier recombination. Importantly, it is also possible to construct a Z-scheme overall water splitting system using the optimized Y 2 Ti 2 O 5 S 2 in combination with surface-modified BiVO 4 in the presence of [Fe(CN) 6 ] 3-/4- , yielding a solar-to-hydrogen energy conversion efficiency of 0.19%. This work provides insights into precise surface modifications of narrow-bandgap photocatalysts as a means of improving the solar water splitting process., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Quantum-dot (QD) light-emitting diodes (QLEDs) are promising candidates for future display technology. An imbalance in the injection of electrons and holes into QLEDs leads to the accumulation of excess charges, predominantly electrons, in the QDs. The precise effects of these accumulated electrons have not yet been fully quantified. This study examines how electron accumulation affects QLED efficiency by operating multiple QLEDs at the same voltage and analyzing the correlation between device efficiency and the number of accumulated electrons, as measured by using electrically pumped transient absorption technology. We analyzed 186 QLED devices made with QDs of different colors and quantum yields. Our results show that when QLEDs utilize QDs with a quantum yield of 95%, electron accumulation indeed reduces device efficiency. However, in QLEDs using QDs with a quantum yield below 70%, a higher density of accumulated electrons enhances the device efficiency.

In this work, we comprehensively investigate the generation of higher harmonic (HH) electric fields normal to the applied rf electric field in multipactor-coexisting plasma breakdown by fully kinetic particle-in-cell (PIC) simulations and a theoretical model. Firstly, a base case at driving frequency 1 GHz, transverse rf electric field amplitude 3 MV mâˆ'1, and background gas pressure 0.2 Torr, is studied in detail. The enhanced harmonic frequency observed is around ten times the fundamental rf frequency, significantly lower than the Langmuir frequency. A theoretical model reveals that the fundamental mechanism of HHs generation is streamâ€"plasma instability, which originates from stream-like secondary electron emission interacting with plasma. The resulting HH frequency and the growth rate of its oscillating amplitude from the theoretical model, agree well with the PIC simulations. With increasing pressure, the HH oscillations are found to be significantly reduced. This is because at higher pressure the gas ionization rate is higher, which causes a more rapidly increasing plasma density, leaving less time for the growth of instability. Furthermore, the parameter space in terms of background gas pressure and rf field amplitude within which the HHs appear is revealed. Finally, the effect of the driving rf frequency on HHs is also investigated, and it is found that the instability-induced oscillating HHs field remains when the driving frequency is increased to 2 GHz, however, it is highly reduced at higher driving frequency of 5 GHz, as oscillations at the fundamental frequency start playing a more important role. [ABSTRACT FROM AUTHOR]

Alloying is an important strategy in tailoring the functionality of materials. In metal nanoclusters (NCs), the introduction of a heterometal leads to alloy nanoclusters that often outperform the homometal ones in terms of the physical and chemical properties. In this work, a series of four M144(PET)60 alloy NCs (where, M = Au/Ag, PET = −SCH2CH2Ph) are synthesized and characterized. The silver doping into the homogold template (Au144) leads to more prominent optical absorption features in the steady-state spectrum in the visible range. Femtosecond transient absorption spectroscopy reveals the effect of Ag doping on the electronic relaxation dynamics compared to Au144 and the pump fluence independent dynamics. Electrochemical results reflect a narrowing of HOMO—LUMO gap (Eg) induced by Ag doping. A temperature dependence of the single-electron charging is also observed for the series of alloy NCs, in which the Eg values of the alloy NCs enlarge as the temperature decreases, which is characteristic of semiconducting behavior. [ABSTRACT FROM AUTHOR]

State transition in the multiple-levels system has the great potential applications in the quantum technology. In this article we employ a deterministic approach in complex space to analyze the dynamics of the 1s–2p electron transition in the hydrogen atom. The electron's spin motion is embodied in the framework of quantum Hamilton mechanics that allows us to examine the transition dynamics more precisely. The transition is driven by an oscillating electric field in the z-direction. The electron's transition process can be visualized by monitoring its motion in the complex space. The quantum potential and the total energy proposed in this paper provide new indices to observe the dynamic changes of electrons in the transition process. [ABSTRACT FROM AUTHOR]

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[Display omitted] • The electron population near the conduction band minimum of InSb includes two different-laser-fluence-dependent growth processes. • The effects of varying the pump fluence on the band gap of InSb were systematically investigated. • The electrostatic field on the surface of InSb can be dressed by medium ultrafast pulsed lasers. Studying ultrafast dynamical processes is essential for understanding light-matter coupling, which is crucial for the optoelectronic and photonic applications of semiconductor materials. Herein, we investigate the evolution of electron population near the conduction band minimum (CBM) and band gap in InSb (100) crystal under different laser fluences using time- and angle-resolved photoelectron spectra (TrARPES). In contrast to the pump-fluence-independent fast growth process (FP) of the electron population, the slow process (SP) is fluence sensitive, which is similar to the temperature-dependent behavior observed in InSb (110). In addition, we observe a band gap enlargement with increasing the photoexcitation flux. Comprehensive analysis reveals that these observed diverse results are attributed to the laser-tunable dielectric function on the surface of InSb. Our findings not only enhance the understanding of laser-semiconductor interactions but also broaden the potential applications in the field of optoelectronic and photonic devices. [ABSTRACT FROM AUTHOR]

A model to predict the electron transmission probability from the random impurity distribution in a two-dimensional nanowire system by combining the time evolution of the electron wave function and machine learning is proposed. We have shown that the intermediate state of the time evolution calculation is advantageous for efficient modeling by machine learning. The features for machine learning are extracted by analyzing the time variation of the electron density distribution using time evolution calculations. Consequently, the prediction error of the model is improved by performing machine learning based on the features. The proposed method provides a useful perspective for analyzing the motion of electrons in nanoscale semiconductors. [ABSTRACT FROM AUTHOR]

Attosecond science has paved the way for direct probing of electron dynamics in gases and solids. This review provides an overview of recent attosecond measurements, focusing on the wealth of knowledge obtained by the application of isolated attosecond pulses in studying dynamics in gases and solid-state systems. Attosecond photoelectron and photoion measurements in atoms reveal strong-field tunneling ionization and a delay in the photoemission from different electronic states. These measurements applied to molecules have shed light on ultrafast intramolecular charge migration. Similar approaches are used to understand photoemission processes from core and delocalized electronic states in metal surfaces. Attosecond transient absorption spectroscopy is used to follow the real-time motion of valence electrons and to measure the lifetimes of autoionizing channels in atoms. In solids, it provides the first measurements of bulk electron dynamics, revealing important phenomena such as the timescales governing the switching from an insulator to a metallic state and carrier-carrier interactions.

Photocatalysis with plasmonic nanostructures has lately emerged as a transformative paradigm to drive and alter chemical reactions using light. At the surface of metallic nanoparticles, photoexcitation results in strong near fields, short-lived high-energy "hot" carriers, and light-induced heating, thus creating a local environment where reactions can occur with enhanced efficiencies. In this context, it is critical to understand how to manipulate the nonequilibrium processes triggered by light, as their ultrafast (femto- to picoseconds) relaxation dynamics compete with the process of energy transfer toward the reactants. Accurate predictions of the plasmon photocatalytic activity can lead to optimized nanophotonic architectures with enhanced selectivity and rates, operating beyond the intrinsic limitations of the steady state. Here, we report on an original modeling approach to quantify, with space, time, and energy resolution, the ultrafast energy exchange from plasmonic hot carriers (HCs) to molecular systems adsorbed on the metal nanoparticle surface while consistently accounting for photothermal bond activation. Our analysis, illustrated for a few typical cases, reveals that the most energetic nonequilibrium carriers (i.e., with energies well far from the Fermi level) may introduce a wavelength-dependence of the reaction rates, and it elucidates on the role of the carriers closer to the Fermi energy and the photothermally heated lattice, suggesting ways to enhance and optimize each contribution. We show that the overall reaction rates can benefit strongly from using pulsed illumination with the optimal pulse width determined by the properties of the system. Taken together, these results contribute to the rational design of nanoreactors for pulsed catalysis, which calls for predictive modeling of the ultrafast HC-hot adsorbate energy transfer.

Flapping of the current sheet (CS) associated with the propagation of high‐velocity bulk flows allowed to observe the super thin current sheet (STCS) in the magnetotail plasma sheet (PS). During the interval of interest, 111 crossings of the CS neutral plane were detected. In 95 crossings, the STCSs with a current density J ≥ 20 nA/m2 were observed. A half‐thickness (LSTCS) of the STCSs was about a few electron gyroradii or less. In a number of the STCSs the parameter of adiabaticity (κe) was <1.0 for suprathermal electron population (>1 keV). Our analysis has shown that the electric current in such STCSs is carried by unmagnetized electrons (κe < 1), and the stress balance is supported by the off‐diagonal terms of their pressure tensor. In this sense, the underlying physics of the formation of STCSs at electron scales by unmagnetized electrons is similar to the mechanism of ion‐scale thin CS formation by the quasi‐adiabatic ions. The low‐energy population of magnetized electrons is also crucially important since it keeps the STCS stable and allows their observation as a quasi‐stationary structure. We compare the observed half‐thickness of the STCS with that predicted by a new kinetic theory (λ) considering the coupling between ion‐scale TCS and electron‐scale STCS. We found a reasonable agreement between both values: LSTCS ∼ (0.3–1)λ. Further improvement in the theory taking into account the dynamics of unmagnetized electrons may provide better agreement with observations. Key Points: Super thin current sheets (STCSs) with half‐thickness about few electron gyroradii or less are observed during high‐velocity bulk flowsIn the STCSs, the current is carried by unmagnetized electrons and stress balance is supported by off‐diagonal terms of their pressure tensorIn the STCSs, the higher energy electrons carry the current, while the low‐energy electrons support the stability of the STCS [ABSTRACT FROM AUTHOR]

In Earth's foreshock, there are many foreshock transients that have core regions with low field strength, low density, high temperature, and bulk velocity variation. Through dynamic pressure perturbations, they can disturb the magnetosphere–ionosphere system. They can also accelerate particles contributing to particle acceleration at the bow shock. Recent Magnetospheric Multiscale (MMS) mission observations showed that inside the low field strength core region, there are usually kinetic‐scale magnetic holes with even lower field strength (<1 nT). However, their nature and effects are unknown. In this study, we used MMS observations to conduct case studies on these magnetic holes. We found that they could be subion‐scale current sheets without a magnetic normal component and guide field, driven by the motion of demagnetized electrons. These magnetic holes can also be subion‐scale flux ropes or magnetic helical structures with weak axial field. The low field strength inside them can be either driven by external expansion or electron mirror mode. Electrons inside them show flux depletion at 90° pitch angle resulting in an "electron hole" distribution. These magnetic holes can play a role in electron dynamics, wave excitation, and shaping the foreshock transient structures. Our detailed study of such features sheds light on the turbulent nature of foreshock transient cores. Key Points: We identified the nature of kinetic‐scale magnetic holes inside foreshock transients, which can be subion‐scale current sheetsThey can also be flux ropes with low field strength inside them due to external expansion or electron mirror modeThey could help shape magnetic profile and play a role in turbulence, electron dynamics, and wave excitation inside foreshock transients [ABSTRACT FROM AUTHOR]

A detailed analysis of the electronic structure and decay dynamics in a symmetric system with three electrons in three linearly aligned binding sites representing quantum dots (QDs) is given. The two outer A QDs are two-level potentials and can act as (virtual) photon emitters, whereas the central B QD can be ionized from its one level into a continuum confined on the QD axis upon absorbing virtual photons in the inter-Coulombic decay (ICD) process. Two scenarios in such an ABA array are explored. One ICD process is from a singly excited resonance state, whose decay releasing one virtual photon we find superimposed with resonance energy transfer among both A QDs. Moreover, the decay-process manifold for a doubly excited (DE) resonance is explored, in which collective ICD among all three sites and excited ICD among the outer QDs engage. Rates for all processes are found to be extremely low, although ICD rates with two neighbors are predicted to double compared to ICD among two sites only. The slowing is caused by Coulomb barriers imposed from ground or excited state electrons in the A sites. Outliers occur on the one hand at short distances, where the charge transfer among QDs mixes the possible decay pathways. On the other hand, we discovered a shape resonance-enhanced DE-ICD pathway, in which an excited and localized B* shape resonance state forms, which is able to decay quickly into the final ICD continuum.