Electronic Nonadiabatic Dynamics Research Articles

Effects of BPQ binding on the nonadiabatic dynamics of excited electrons in poly(dG)-poly(dC) DNA under proton irradiation.

The interaction between DNA and small molecules is important for understanding the mechanisms of DNA-based multifunctional devices and has been extensively studied. However, there are few reports on such interactions in irradiation environments. Here, we investigate the nonadiabatic dynamic behaviors of excited electrons in double-stranded DNA bound to BPQ molecule upon proton irradiation, focusing on the energy deposition and electronic excitation dynamics as protons traverse the DNA along different channels. Our results reveal that the presence of BPQ significantly influences charge migration and DNA damage, with notable differences between CGvdW and CGcovalent adducts. The energy deposition process is highly dependent on charge density, and guanine exhibits higher excitation propensity than cytosine due to its structural characteristics. The BPQ molecule enhances DNA charge migration and promotes damage through secondary electron migration. These findings provide insights into the nonadiabatic dynamics of DNA under ionizing radiation and have implications for designing targeted electrophilic organics to improve radiotherapy efficacy.

Non-adiabatic ring polymer molecular dynamics in the phase space of the SU(N) Lie group.

We derive the non-adiabatic ring polymer molecular dynamics (RPMD) approach in the phase space of the SU(N) Lie Group. This method, which we refer to as the spin mapping non-adiabatic RPMD (SM-NRPMD), is based on the spin-mapping formalism for the electronic degrees of freedom (DOFs) and ring polymer path-integral description for the nuclear DOFs. Using the Stratonovich-Weyl transform for the electronic DOFs and the Wigner transform for the nuclear DOFs, we derived an exact expression of the Kubo-transformed time-correlation function (TCF). We further derive the spin mapping non-adiabatic Matsubara dynamics using the Matsubara approximation that removes the high frequency nuclear normal modes in the TCF and derive the SM-NRPMD approach from the non-adiabatic Matsubara dynamics by discarding the imaginary part of the Liouvillian. The SM-NRPMD method has numerical advantages compared to the original NRPMD method based on the Meyer-Miller-Stock-Thoss (MMST) mapping formalism due to a more natural mapping using the SU(N) Lie Group that preserves the symmetry of the original system. We numerically compute the Kubo-transformed position auto-correlation function and electronic population correlation function for three-state model systems. The numerical results demonstrate the accuracy of the SM-NRPMD method, which outperforms the original MMST-based NRPMD. We envision that the SM-NRPMD method will be a powerful approach to simulate electronic non-adiabatic dynamics and nuclear quantum effects accurately.

Complex-valued derivative propagation method with adaptive moving grids for electronic nonadiabatic dynamics

The coupled complex quantum Hamilton–Jacobi equations in the diabatic representation are solved on adaptive moving grids for electronic nonadiabatic dynamics. Substitution of the wave functions in exponential form into the coupled time-dependent Schrödinger equations yields the coupled complex quantum Hamilton–Jacobi equations. Analytic equations of motion are derived for the spatial derivatives of the complex action functions for both surfaces. The equations of motion for the complex actions and their spatial derivatives are converted into the arbitrary Lagrangian–Eulerian frame, allowing us to have many ways to choose the velocities for the moving points. The grid points can be specified to move along with the probability fluid. In contrast, choosing the boundary grid points to follow Lagrangian trajectories and forcing the internal grid points to be equally spaced at each time step, we obtain a moving structured grid of uniform spacing during the wave packet evolution. Several examples are presented to illustrate main features of the adaptive grid method, including a single avoided crossing system, a dual avoided crossing system, an ultrashort laser pulse excitation system, and a three-dimensional nonadiabatic system. Accurate computational results demonstrate that the adaptive grid method provides an alternative way to study electronic nonadiabatic dynamics.

High-order harmonic generation from stretched C2H2 molecules in intense laser fields

We investigate the high harmonic generation from stretched acetylene molecules subjected to intense laser fields employing time-dependent Hartree-Fock methods. It is found that as the C-C and C-H bonds are stretched, the harmonic efficiency increases significantly due to the increased ionization of inner valence $\ensuremath{\sigma}$ orbitals in the monochromatic field, while the harmonic yield will be limited by the strong depletion of the ground-state population under a certain bond length. Moreover, the harmonic emission is affected by the nonadiabatic electron dynamics from the multiorbital coupling effects. In addition, by introducing a two-color field scheme for different C-H bond configurations with the fixed C-C bond, the aforementioned harmonic efficiency will be further enhanced due to laser-induced strong excitation from inner valence orbitals to initially unoccupied orbitals. The above results would be helpful for further understanding multiorbital dynamics in the harmonic generation from polyatomic molecules.

Moving boundary truncated grid method for electronic nonadiabatic dynamics.

The moving boundary truncated grid method is developed to study the wave packet dynamics of electronic nonadiabatic transitions between a pair of diabatic potential energy surfaces. The coupled time-dependent Schrödinger equations (TDSEs) in the diabatic representation are integrated using adaptive truncated grids for both the surfaces. As time evolves, a variable number of grid points fixed in space are activated and deactivated without any advance information of the wave packet dynamics. Essential features of the truncated grid method are first illustrated through applications to three one-dimensional model problems, including the systems of single avoided crossing, dual avoided crossing, and extended coupling region with reflection. As a demonstration for chemical applications, the truncated grid method is then employed to study the dynamics of photoisomerization of retinal in rhodopsin described by a two-electronic-state two-dimensional model. To demonstrate the capability of the truncated grid method to deal with the electronic nonadiabatic problem in high dimensionality, we consider a multidimensional electronic nonadiabatic system in two, three, and four dimensions. The results indicate that the correct grid points are automatically activated to capture the growth and decay of the wave packets on both of the surfaces. Therefore, the truncated grid method greatly decreases the computational effort to integrate the coupled TDSEs for multidimensional electronic nonadiabatic systems.

Simulation of the photodetachment spectra of the nitrate anion (NO3-) in the B̃ 2E' energy range and non-adiabatic electronic population dynamics of NO3.

The photodetachment spectrum of the nitrate anion (NO3-) in the energy range of the NO3 second excited state is simulated from first principles using quantum wave packet dynamics. The prediction at 10 K and 435 K relies on the use of an accurate full-dimensional fully coupled five state diabatic potential model utilizing an artificial neural network. The ability of this model to reproduce experimental spectra was demonstrated recently for the lower energy range [A. Viel, D. M. G. Williams and W. Eisfeld, J. Chem. Phys. 2021, 154, 084302]. Analysis of the spectra indicates a weaker Jahn-Teller coupling compared to the first excited state. The detailed non-adiabatic dynamics is studied by computing the population dynamics. An ultra-fast non-statistical radiationless decay is found only among the Jahn-Teller components, which is followed by a slow statistical non-radiative decay among the different state manifolds. The latter is reproduced perfectly by a simple first order kinetics model. The dynamics in the second excited state is not affected by the presence of a conical intersection with the first excited state manifold.

Unraveling energy and charge transfer in type-II van der Waals heterostructures

Recent experiments observed significant energy transfer in type-II van der Waals (vdW) heterostructures, such as WS2/MoSe2, which is surprising due to their staggered band alignment and weak spectral overlap. In this work, we carry out first-principles calculations to shed light on energy and charge transfer in WS2/MoSe2 heterostructure. Incorporating excitonic effect in nonadiabatic electronic dynamics, our first-principles calculations uncover a two-step process in competing energy and charge transfer, unravel their relative efficiencies and explore the means to control their competition. While both Dexter and Förster mechanisms can be responsible for energy transfer, they are shown to operate at different conditions. The excitonic effect is revealed to drive ultrafast energy and charge transfer in type-II WS2/MoSe2 heterostructure. Our work provides a comprehensive picture of exciton dynamics in vdW heterostructures and paves the way for rational design of novel vdW heterostructures for optoelectronic and photovoltaic applications.

Equilibrium properties of warm dense deuterium calculated by the wave packet molecular dynamics and density functional theory method.

A joint simulation method based on the wave packet molecular dynamics and density functional theory (WPMD-DFT) is applied to study warm dense deuterium (nonideal deuterium plasmas). This method was developed recently as an extension of the wave packet molecular dynamics (WPMD) in which the equations of motion are solved simultaneously for classical ions and semiclassical electrons represented as Gaussian wave packets. Compared to the classical molecular dynamics and WPMD simulations, the method of WPMD-DFT provides a more accurate representation of quantum effects such as electron-ion coupling and electron degeneracy. It allows studying nonadiabatic dynamics of electrons and ions in equilibrium and nonequilibrium states while being more accurate and efficient at high densities than WPMD and classical molecular dynamics. In the paper, we discuss particular features of the method such as special boundary conditions and the procedure of isentrope calculation as well as the results obtained by WPMD-DFT for the shock-compressed deuterium. The compression isentrope and principal Hugoniot curves obtained by WPMD-DFT are compared with available experimental data and other simulation approaches to validate the method. It opens up a possibility of further application of the method to study nonequilibrium states and relaxation processes.

Effect of collisions on non-adiabatic electron dynamics in ITG-driven microturbulence

Non-adiabatic electron response leads to significant changes in ion temperature gradient (ITG) eigenmodes, leading, in particular, to fine-structures that are significantly extended along the magnetic field lines at corresponding mode rational surfaces (MRSs). These eigenmodes can nonlinearly interact with themselves to drive zonal flows via the so-called self-interaction mechanism. In this paper, the effect of collisions on these processes are studied. In the presence of non-adiabatic electrons, the linear growth rate of ITG eigenmodes decreases with the increasing collisionality. Detailed velocity space analysis of the distribution function shows that this results from collisions leading to a more adiabatic-like response of electrons away from MRSs. In linear simulations, collisions are furthermore found to broaden the radial width of the fine-structures, which translates to narrower tails of the eigenmode in extended ballooning space. The characteristic parallel scale length associated with these tails is shown to scale with the mean free path of electrons. In nonlinear turbulence simulations accounting for physically relevant values of collisionality, the fine-structures located at MRSs, together with the associated drive of zonal flows via self-interaction, are shown to persist and play a significant role.

Dissipative electronic nonadiabatic dynamics within the framework of the Schrödinger–Langevin equation

Dissipative electronic nonadiabatic dynamics within the framework of the Schrödinger–Langevin equation

Electron Dynamics in Molecular Elementary Processes and Chemical Reactions

Abstract This account places a particular emphasis on recent progress in the theory and its applications of nonadiabatic electron dynamics in chemical science. After a brief description of the fundamental relevance of the breakdown of the Born-Oppenheimer approximation, we show examples of our extensive and systematic application of electron dynamics to highlight the significance and necessity of beyond-Born-Oppenheimer chemistry. The chemical subjects presented herewith cover (1) characteristic phenomena arising from nonadiabatic dynamics, (2) flow of electrons during chemical reactions and ionization dynamics, (3) symmetry breaking and its possible control in chemical reactions emerging from multi-dimensional nonadiabatic interactions, a special example which can cause possible breakdown of molecular mirror symmetry, (4) physical mechanism of charge separation in organic compounds and biomolecules, (5) essential roles of charge separation and elementary chemical reaction mechanisms in catalytic cycles of Mn oxo complexes up to Mn4CaO5 in water splitting dynamics (2H2O → 4H+ + 4e− + O2), (6) chemical bonds and huge electronic state fluctuation in densely quasi-degenerate electronic manifolds, which make chemistry without the notion of potential energy surfaces, and so on. All these materials and issues have been chosen because they are not directly resolved by the method of energetics based on time-independent quantum chemistry. We thus have been exploring, developing, and cultivating a new chemical realm beyond the Born-Oppenheimer paradigm. This account is closed with a scope about the theory of simultaneous electronic and nuclear quantum wavepacket dynamics.

Non-adiabatic quantum dynamics without potential energy surfaces based on second-quantized electrons: Application within the framework of the MCTDH method.

A first principles quantum formalism to describe the non-adiabatic dynamics of electrons and nuclei based on a second quantization representation (SQR) of the electronic motion combined with the usual representation of the nuclear coordinates is introduced. This procedure circumvents the introduction of potential energy surfaces and non-adiabatic couplings, providing an alternative to the Born-Oppenheimer approximation. An important feature of the molecular Hamiltonian in the mixed first quantized representation for the nuclei and the SQR representation for the electrons is that all degrees of freedom, nuclear positions and electronic occupations, are distinguishable. This makes the approach compatible with various tensor decomposition Ansätze for the propagation of the nuclear-electronic wavefunction. Here, we describe the application of this formalism within the multi-configuration time-dependent Hartree framework and its multilayer generalization, corresponding to Tucker and hierarchical Tucker tensor decompositions of the wavefunction, respectively. The approach is applied to the calculation of the photodissociation cross section of the HeH+ molecule under extreme ultraviolet irradiation, which features non-adiabatic effects and quantum interferences between the two possible fragmentation channels, He + H+ and He+ + H. These calculations are compared with the usual description based on ab initio potential energy surfaces and non-adiabatic coupling matrix elements, which fully agree. The proof-of-principle calculations serve to illustrate the advantages and drawbacks of this formalism, which are discussed in detail, as well as possible ways to overcome them. We close with an outlook of possible application domains where the formalism might outperform the usual approach, for example, in situations that combine a strong static correlation of the electrons with non-adiabatic electronic-nuclear effects.

Reducing Anomalous Hysteresis in Perovskite Solar Cells by Suppressing the Interfacial Ferroelectric Order.

Despite the booming research in organometal halide perovskite solar cells (PSCs) of recent years, considerable roadblocks remain for their large-scale deployment, ranging from undesirable current-voltage hysteresis to inferior device stability. Among various plausible origins of hysteresis, interfacial ferroelectricity is particularly intriguing and warrants a close scrutiny. Here, we examine interfacial ferroelectricity in MAPbI3 (FAPbI3)/TiO2 and MAPbI3/phenyl-C61-butyric-acid-methyl-ester (PCBM) heterostructures and explore the correlations between the interfacial ferroelectricity and the hysteresis from the perspective of nonadiabatic electronic dynamics. It is found that the ferroelectric order develops at the MAPbI3/TiO2 interface owing to the interaction between the polar MA ions and TiO2. The polarization switching of the MA ions under an applied gate field would drastically result in different rates in interfacial photoelectron injection and electron-hole recombination, contributing to the undesirable hysteresis. In sharp contrast, ferroelectricity is suppressed at the FAPbI3/TiO2 and MAPbI3/PCBM interfaces, thanks to elimination of the interfacial electric field between perovskite and TiO2 via substitution of strong polar MA (dipole moment: 2.29 debye) by weak polar FA ions (dipole moment: 0.29 debye) and interface passivation, leading to consistent interfacial electronic dynamics and the absence of hysteresis. The present work sheds light on the physical cause for hysteresis and points to the direction to which the hysteresis could be mitigated in PSCs.

Nonadiabatic electron dynamics in time-dependent density functional theory at the cost of adiabatic local density approximation

We propose a computationally efficient approach to the nonadiabatic time-dependent density functional theory (TDDFT) which is based on a representation of the frequency-dependent exchange correlation kernel as a response of a set of damped oscillators. The requirements to computational resources needed to implement our approach do not differ from those of the standard real-time TDDFT in the adiabatic local density approximation (ALDA). Thus, our result offers an exciting opportunity to take into account temporal nonlocality and memory effects in calculations with TDDFT in quantum chemistry and solid state physics for unprecedentedly low costs.

Nonadiabatic Electron Dynamics in Tunneling Junctions: Lattice Exchange-Correlation Potential.

The search for exchange-correlation functionals going beyond the adiabatic approximation has always been a challenging task for time-dependent density-functional theory. Starting from known results and using symmetry properties, we put forward a nonadiabatic exchange-correlation functional for lattice models describing a generic transport setup. We show that this functional reduces to known results for a single quantum dot connected to one or two reservoirs and furthermore yields the adiabatic local-density approximation in the static limit. Finally, we analyze the features of the exchange-correlation potential and the physics it describes in a linear chain connected to two reservoirs where the transport is induced by a bias voltage applied to the reservoirs. We find that the Coulomb blockade is correctly described for a half-filled chain, while additional effects arise as the doping of the chain changes.

Relativistic formalism of nonadiabatic electron-nucleus-radiation dynamics in molecules: Path-integral approach

Many-electron relativistic quantum theories of stationary molecular electronic states have been developed in so-called quantum chemistry, in which nuclear configuration is frozen in space-time under the Born-Oppenheimer approximation. These time-independent methods are concerned with energetics, which are supposed to determine molecular structures and dominate low-energy chemical reactions. Yet, rapid progress in laser technology demands that theoretical chemistry should get prepared for relativistic electron-nucleus coupled dynamics driven by unconventional ultrastrong laser pulses. We therefore generalize our previously developed path-integral formalism of nonadiabatic electron dynamics [Hanasaki and Takatsuka, Phys. Rev. A 81, 052514 (2010)] to cover the relativistic regime in radiation fields. Starting from a formal relativistic path-integral formulation of electron-nucleus coupled systems interacting with quantum radiation fields, we reduce it to a tractable level of approximations to set a theoretical foundation for future applications.

State dependent ring polymer molecular dynamics for investigating excited nonadiabatic dynamics

A recently proposed nonadiabatic ring polymer molecular dynamics (NRPMD) approach has shown to provide accurate quantum dynamics by incorporating explicit state descriptions and nuclear quantizations. Here, we present a rigorous derivation of the NRPMD Hamiltonian and investigate its performance on simulating excited state nonadiabatic dynamics. Our derivation is based on the Meyer-Miller-Stock-Thoss mapping representation for electronic states and the ring-polymer path-integral description for nuclei, resulting in the same Hamiltonian proposed in the original NRPMD approach. In addition, we investigate the accuracy of using NRPMD to simulate the photoinduced nonadiabatic dynamics in simple model systems. These model calculations suggest that NRPMD can alleviate the zero-point energy leakage problem that is commonly encountered in the classical Wigner dynamics and provide accurate excited state nonadiabatic dynamics. This work provides a solid theoretical foundation of the promising NRPMD Hamiltonian and demonstrates the possibility of using the state-dependent RPMD approach to accurately simulate electronic nonadiabatic dynamics while explicitly quantizing nuclei.

Monitoring of Nonadiabatic Effects in Individual Chromophores by Femtosecond Double-Pump Single-Molecule Spectroscopy: A Model Study.

We explore, by theoretical modeling and computer simulations, how nonadiabatic couplings of excited electronic states of a polyatomic chromophore manifest themselves in single-molecule signals on femtosecond timescales. The chromophore is modeled as a system with three electronic states (the ground state and two non-adiabatically coupled excited states) and a Condon-active vibrational mode which, in turn, is coupled to a harmonic oscillator heat bath. For this system, we simulate double-pump single-molecule signals with fluorescence detection for different system-field interaction strengths, from the weak-coupling regime to the strong-coupling regime. While the signals are determined by the coherence of the electronic density matrix in the weak-coupling regime, they are determined by the populations of the electronic density matrix in the strong-coupling regime. As a consequence, the signals in the strong coupling regime allow the monitoring of nonadiabatic electronic population dynamics and are robust with respect to temporal inhomogeneity of the optical gap, while signals in the weak-coupling regime are sensitive to fluctuations of the optical gap and do not contain information on the electronic population dynamics.

Nonadiabatic dynamics of electrons and atoms under nonequilibrium conditions

An approach to non-adiabatic dynamics of atoms in molecular and condensed matter systems under general non-equilibrium conditions is proposed. In this method interaction between nuclei and electrons is considered explicitly up to the second order in atomic displacements defined with respect to the mean atomic trajectory. This method enables one to consider movement of atoms beyond their simple vibrations. Both electrons and nuclei are treated fully quantum-mechanically using a combination of path integrals applied to nuclei and non-equilibrium Green's functions (NEGF) to elections. Our method is partition-less: initially, the entire system is coupled and assumed to be at thermal equilibrium. Then, the exact application of the Hubbard-Stratanovich transformation in mixed real and imaginary times enables us to obtain, without doing any additional approximations, an exact expression for the reduced density matrix for nuclei and hence an effective quantum Liouville equation for them, both containing Gaussian noises. It is shown that the time evolution of the expectation values for atomic positions is described by an infinite hierarchy of stochastic differential equations for atomic positions and momenta and their various fluctuations. The actual dynamics is obtained by sampling all stochastic trajectories. It is expected that applications of the method may include photo-induced chemical reactions (e.g. dissociation), electromigration, atomic manipulation in scanning tunneling microscopy, to name just a few.

Complex-valued derivative propagation method with approximate Bohmian trajectories: Application to electronic nonadiabatic dynamics

The coupled complex quantum Hamilton-Jacobi equations for electronic nonadiabatic transitions are approximately solved by propagating individual quantum trajectories in real space. Equations of motion are derived through use of the derivative propagation method for the complex actions and their spatial derivatives for wave packets moving on each of the coupled electronic potential surfaces. These equations for two surfaces are converted into the moving frame with the same grid point velocities. Excellent wave functions can be obtained by making use of the superposition principle even when nodes develop in wave packet scattering.