Ab initio nonadiabatic molecular dynamics study on spin–orbit coupling induced spin dynamics in ferromagnetic metals

Understanding the photoexcitation induced spin dynamics in ferromagnetic metals is important for the design of photo-controlled ultrafast spintronic device.In this work,by the ab initio nonadiabatic molecular dynamics simulation,we have studied the spin dynamics induced by spin–orbit coupling(SOC)in Co and Fe using both spin-diabatic and spin-adiabatic representations.In Co system,it is found that the Fermi surface(E_(F))is predominantly contributed by the spin-minority states.The SOC induced spin flip will occur for the photo-excited spin-majority electrons as they relax to the E_(F),and the spin-minority electrons tend to relax to the EFwith the same spin through the electron–phonon coupling(EPC).The reduction of spin-majority electrons and the increase of spin-minority electrons lead to demagnetization of Co within100 fs.By contrast,in Fe system,the E_(F) is dominated by the spin-majority states.In this case,the SOC induced spin flip occurs for the photo-excited spin-minority electrons,which leads to a magnetization enhancement.If we move the E_(F) of Fe to higher energy by 0.6eV,the E_(F) will be contributed by the spin-minority states and the demagnetization will be observed again.This work provides a new perspective for understanding the SOC induced spin dynamics mechanism in magnetic metal systems.

Exact solution of slow quench dynamics and nonadiabatic characterization of topological phases

Previous studies have shown that the bulk topology of single-particle systems can be captured by the band inversion surface or by the spin inversion surface emerging on the time-averaged spin polarization.Most of the studies,however,are based on the single-particle picture even though the systems are fermionic and multi-bands.Here,we study the slow quench dynamics of topological systems with all the valence bands fully occupied,and show that the concepts of band inversion surface and spin inversion surface are still valid.More importantly,the many-particle nonadiabatic quench dynamics is shown to be reduced to a new and nontrivial three-level Landau-Zener model.This nontrivial three-level Landau-Zener problem is then solved analytically by applying the integrability condition and symmetry considerations,and thus adds a new member to the few models that are exactly solvable.Based on the analytical results,the topological spin texture revealed by the time-averaged spin polarization can be applied to characterize the bulk topology and thus provides a direct comparison for future experiments.

On-the-Fly Nonadiabatic Dynamics of Caffeic Acid Sunscreen Compound

As a widely-used sunscreen com-pound,the caffeic acid(CA)shows the strong UV absorption,while the photoinduced reaction mecha-nisms behind its photoprotection ability are not fully understood.We try to investigate the photoin-duced internal conversion dynam-ics of CA in order to explore the photoprotection mechanism.The most stable CA isomer is selected to examine its nonadiabatic dy-namics using the on-the-fly surface hopping simulations at the semi-empirical level of electronic-struc-ture theory.The dynamics starting from different electronic states are simulated to explore the dependence of the photoinduced reaction channels on the excitation wavelengths.Several S1/S0 conical intersections,driven by the H-atom detachments and the ring deformations,have been found to be responsible for the nonadiabatic decay of the CA.The simulation re-sults show that the branching ratios towards these intersections are modified by the light with different excitation energies.This provides the valuable information for the understanding of the photoprotection mechanism of the CA compound.

The instability of electrostatic wave in a magnetized dusty plasma with nonadiabatic dust charge fluctuation

The effects of external magnetized field and nonadiabatic dust charge fluctuation on instability of wave incorporating the nonthermally distributed ions and the temperatures of ion and dust in dusty plasmas are investigated. A linear dispersion relation is obtained. The numerical results show that the external magnetized field, fast ions and nonadiabatic dust charge fluctuation have strong influence on the frequency and the damping of wave.

A Theoretical Study on Nonadiabatic Trapping Models of the Reaction NH+H←→N+H_2

The properties of nonadiabatic trapping models of the reaction NH+H -N+H, are investigated in a collinear model as \veil as a non-collinear thermal reaction on the basis of theintrinsic reaction coordinate (IRC) intbrmation obtained by ah initio calculations at QCISD/631 IG** ie\el. Using the unitied statistical theory fornonadiabatic trapping models. the thermal rateconstants over the temperature range of 2000-3000K are computed which are in excellent agreementwith the experiment results.

Nonadiabatic Effect on the Rescattering Trajectories of Electrons in Strong Laser Field Ionization Process

The important features of the rescattering trajectories in strong field ionization process such as the cutoff of the return energy at 3.17Up and that of the final energy at 10Up are obtained, based on the adiabatic approximation in which the initial momentum of the electron is assumed to be zero. We theoretically study the nonadiabatic effect by assuming a nonzero initial momentum on the rescattering trajectories based on the semiclassical simpleman model. We show that the nonzero initial momentum will modify both the maximal return energy at collision and the final energy after backward scattering, but in different ways for odd and even number of return trajectories. The energies are increased for even number of returns but are decreased for odd number of returns when the nonzero （positive or negative） initial momentum is applied.

Nonadiabatic Population Transfer in a Tangent-Pulse Driven Quantum Model

Fine control of the dynamics of a quantum system is the key element to perform quantum information processing and coherent manipulations for atomic and molecular systems. We propose a control protocol using a tangentpulse driven model and demonstrate that it indicates a desirable design, i.e., of being both fast and accurate for population transfer. As opposed to other existing strategies, a remarkable character of the present scheme is that high velocity of the nonadiabatic evolution itself not only will not lead to unwanted transitions but also can suppress the error caused by the truncation of the driving pulse.

Ab Initio Nonadiabatic Dynamics of Semiconductor Materials via Surface Hopping Method

Photoinduced carrier dynamic processes are without doubt the main driving force responsible for the efficient performance of semiconductor nanomaterials in applications like photoconversion and photonics.Nevertheless,establishing theoretical insights into these processes is computationally challenging owing to the multiple factors involved in the processes,namely reaction rate,material surface area,material composition etc.Modelling of photoinduced carrier dynamic processes can be performed via nonadiabatic molecular dynamics(NA-MD)methods,which are methods specifically designed to solve the time-dependent Schrodinger equation with the inclusion of nonadiabatic couplings.Among NA-MD methods,surface hopping methods have been proven to be a mighty tool to mimic the competitive nonadiabatic processes in semiconductor nanomaterials,a worth noticing feature is its exceptional balance between accuracy and computational cost.Consequently,surface hopping is the method of choice for modelling ultrafast dynamics and more complex phenomena like charge separation in Janus transition metal dichalcogenides-based van der Waals heterojunction materials.Covering latest stateof-the-art numerical simulations along with experimental results in the field,this review aims to provide a basic understanding of the tight relation between semiconductor nanomaterials and the proper simulation of their properties via surface hopping methods.Special stress is put on emerging state-ot-the-art techniques.By highlighting the challenge imposed by new materials,we depict emerging creative approaches,including high-level electronic structure methods and NA-MD methods to model nonadiabatic systems with high complexity.

Understanding Photolysis of CH_(3)ONO_(2) with on-the-fly Nonadiabatic Dynamics Simulation at the ADC(2) Level

The nonadiabatic dynamics of methyl nitrate(CH_(3)ONO_(2))is studied with the on-the-fy trajectory surface hopping dynamics at the ADC(2)level.The results confirmed the existence of the ultrafast nonadiabatic decay to the electronic ground state.When the dynamics starts from S_(1) and S_(2),the photoproducts are CH_(3)O+NO_(2),consistent with previous results obtained from the experimental studies and theoretical dynamics simulations at more accurate XMS-CASPT2 level.The photolysis products are CH_(3)O+NO_(2) at the ADC(2)level when the dynamics starts from S3,while different photolysis products were obtained in previous experimental and theoretical works.These results demonstrate that the ADC(2)method may still be useful for treating the photolysis mechanism of CH_(3)ONO_(2) at the long-wavelength UV excitation,while great caution should be paid due to its inaccurate performance in the description of the photolysis dynamics at the short-wavelength UV excitation.This gives valuable information to access the accuracy when other alkyl nitrates are treated at the ADC(2)level.

GW/BSE Nonadiabatic Dynamics Simulations on Excited-State Relaxation Processes of Zinc Phthalocyanine-Fullerene Dyads:Roles of Bridging Chemical Bonds

In this work,we employ electronic structure calculations and nonadiabatic dynamics simulations based on many-body Green function and BetheSalpeter equation(GW/BSE)methods to study excited-state properties of a zinc phthalocyanine-fullerene(ZnPcC_(60))dyad with 6-6 and 5-6 configurations.In the former,the initially populated locally excited(LE)state of ZnPc is the lowest S1 state and thus,its subsequent charge separation is relatively slow.In contrast,in the latter,the S1 state is the LE state of C_(60)while the LE state of ZnPc is much higher in energy.There also exist several charge-transfer(CT)states between the LE states of ZnPc and C_(60).Thus,one can see apparent charge separation dynamics during excited-state relaxation dynamics from the LE state of ZnPc to that of C_(60).These points are verified in dynamics simulations.In the first 200 fs,there is a rapid excitation energy transfer from ZnPc to C_(60),followed by an ultrafast charge separation to form a CT intermediate state.This process is mainly driven by hole transfer from C_(60)to ZnPc.The present work demonstrates that different bonding patterns(i.e.5-6 and 6-6)of the C−N linker can be used to tune excited-state properties and thereto optoelectronic properties of covalently bonded ZnPc-C_(60)dyads.Methodologically,it is proven that combined GW/BSE nonadiabatic dynamics method is a practical and reliable tool for exploring photoinduced dynamics of nonperiodic dyads,organometallic molecules,quantum dots,nanoclusters,etc.

AN IMPROVED NONADIABATIC COLLISION MODEL FOR ION-PIR FORMATION PROCESS:A+BC→A^++BC^- Zheng Ting CAI and Yu Guang MU

Hickman's fast nonadiabatic collision model for the ion-pair formation reaction A+BC→A^++BC^- was improved,where the classical trajectory has been represented by solution of motion equation UR=-dV(R)/dR, here V(R)is Morse potential.Employing this model to the CS+O_2→CS^++O_2^-reaction,a satisfactory agreement with experimental data has been obtained.

Linear and nonlinear excitations in complex plasmas with nonadiabatic dust charge fluctuation and dust size distribution

Both linear and nonlinear excitation in dusty plasmas have been investigated including the nonadiabatic dust charge fluctuation and Gaussian size distribution dust particles. A linear dispersion relation and a Korteweg-de Vries-Burgers equation governing the dust acoustic shock waves are obtained. The relevance of the instability of wave and the wave evolution to the dust size distribution and nonadiabatic dust charge fluctuation is illustrated both analytically and numerically. The numerical results show that the Gaussian size distribution of dust particles and the nonadiabatic dust charge fluctuation have strong common influence on the propagation of both linear and nonlinear excitations.

Nonadiabatic dynamics of electron injection into organic molecules

We numerically investigate the injection process of electrons from metal electrodes to one-dimensional organic molecules by combining the extended Su Schrieffer Heeger （SSH） model with a nonadiabatic dynamics method. It is found that a match between the Fermi level of electrodes and the highest occupied molecular orbital （HOMO） or the lowest unoccupied molecular orbital （LUMO） of organic molecules can be greatly affected by the length of the organic chains, which has a great impact on electron injection. The correlation between oligomers and electrodes is found to open more efficient channels for electron injection as compared with that in polymer/electrode structures. For oligomer/electrode structures, we show that the Schottky barrier essentially does not affect the electron injection as the electrode work function is smaller than a critical value work-function electrode. For polymer/electrode structures This means that the Schottky barrier is pinned for a small we find that it is possible for the Fermi level of electrodes to be pinned to the polaronic level. The condition under which the Fermi level of electrodes exceeds the polaronic level of polymers is shown to not always lead to spontneous electron transfer from electrodes to polymers.

Nonadiabatic dynamics of electron injection into organic molecules

We numerically investigate the injection process of electrons from metal electrodes to one-dimensional organic molecules by combining the extended Su–Schrieffer–Heeger (SSH) model with a nonadiabatic dynamics method. It is found that a match between the Fermi level of electrodes and the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO) of organic molecules can be greatly affected by the length of the organic chains, which has a great impact on electron injection. The correlation between oligomers and electrodes is found to open more efficient channels for electron injection as compared with that in polymer/electrode structures. For oligomer/electrode structures, we show that the Schottky barrier essentially does not affect the electron injection as the electrode work function is smaller than a critical value. This means that the Schottky barrier is pinned for a small work-function electrode. For polymer/electrode structures, we find that it is possible for the Fermi level of electrodes to be pinned to the polaronic level. The condition under which the Fermi level of electrodes exceeds the polaronic level of polymers is shown to not always lead to spontaneous electron transfer from electrodes to polymers.

Polaron-assisted nonadiabatic dynamics in protonated TiO_(2) with surface water molecule

We investigated the polaron-assisted nonadiabatic dynamics in protonated TiO_(2),as well as the polaron-H_(2)O coupling and its effects on the relaxation of photogenerated electrons.We observed that different polaron hopping regimes result in varied nonadiabatic couplings and relaxations of excited electrons from the conduction band minimum to the gap states of protonated TiO_(2),with a weak dependence on the actual trapping site of the polaron.Surface-adsorbed H_(2)O molecules can attract polarons toward the adsorbed Ti sites,with the coupling between H_(2)O and the polaron being inversely proportional to their distance.Our findings suggest that the lifetime of the photogenerated charge carriers can be extended by reducing the polaron-H_(2)O distances,with expected benefits to the efficiency of the reduced TiO 2 samples for photocatalytic applications.

Nonadiabatic geometric quantum computation with optimal control on superconducting circuits

Quantum gates,which are the essent ial building blocks of quantum computers,are very fragile.Thus,to realize robust quanturm gates with high fidelity is the ultimate goal of quantum manipulation.Here,we propose a nonadiabatic geometric quantum computation scheme on superconducting circuits to engineer arbitrary quantum gates,which share both the robust merit of geometric phases and the capacity to combine with optimal control technique to further enhance the gate robustness.Specif-ically,in our proposal,arbitrary geometric single-qubit gates can be realized on a transmon qubit,by a resonant microwave field driving,with both the amplitude and phase of the driving being time-dependent.Meanwhile,nontrivial two-qubit gometric gates can be implemented by two capacitively coupled transmon qubits,with one of the transmon qubits'frequency being modulated to obtain ef-fective resonant coupling between them.Therefore,our scheme provides a promising step towards fault-tolerant solid-state quantum computation.

Experimental realization of single-shot nonadiabatic holonomic gates in nuclear spins

Nonadiabatic holonomic quantum computation has received increasing attention due to its robustness against control errors. However, all the previous schemes have to use at least two sequentially implemented gates to realize a general one-qubit gate. Based on two recent reports, we construct two Hamiltonians and experimentally realized nonadiabatic holonomic gates by a single-shot implementation in a two-qubit nuclear magnetic resonance （NMR） system. Two noncommuting one-qubit holonomic gates, rotating along .~ and ~ axes respectively, are implemented by evolving a work qubit and an ancillary qubit nonadiabatically following a quantum circuit designed. Using a sequence compiler developed for NMR quantum information processor, we optimize the whole pulse sequence, minimizing the total error of the implementation. Finally, all the nonadiabatic holonomic gates reach high unattenuated experimental fidelities over 98%.

Nonadiabatic dynamics and geometric phase of an ultrafast rotating electron spin

The spin in a rotating frame has attracted a lot of attentions recently,as it deeply relates to both fundamental physics such as pseudo-magnetic field and geometric phase,and applications such as gyroscopic sensors.However,previous studies only focused on adiabatic limit,where the rotating frequency is much smaller than the spin frequency.Here we propose to use a levitated nano-diamond with a built-in nitrogen-vacancy(NV)center to study the dynamics and the geometric phase of a rotating electron spin without adiabatic approximation.We find that the transition between the spin levels appears when the rotating frequency is comparable to the spin frequency at zero magnetic field.Then we use Floquet theory to numerically solve the spin energy spectrum,study the spin dynamics and calculate the geometric phase under a finite magnetic field,where the rotating frequency to induce resonant transition could be greatly reduced.

Nonadiabatic acceleration of plasma sheet ions related to ion cyclotron waves

The nonadiabatic acceleration of plasma sheet ions is important to the understanding of substorm energetic injections and the formation of ring current. Previous studies show that nonadiabatic acceleration of protons by magnetic field dipolarization is hard to occur at X>–10 RE because the time-scale of dipolarization(several minutes) is much larger than the gyroperiod of protons there(several seconds). In this paper, we present a case of nonadiabatic acceleration of plasma sheet ions observed by Cluster on October 30, 2006 at(XGSM, YGSM)=(-7.7, 4.7) RE. The nonadiabatic acceleration of ions is caused not by previously reported magnetospheric dipolarization but by the ultra low frequency(ULF) waves during magnetospheric dipolarization. The nonadiabatic acceleration of ions generates a new energy flux structure of ions, which is characterized by the usual energy flux increase of ions(28–80 ke V) and a concurrent energy flux decrease of ions in a lower energy range(10 e V–20 ke V). These new observations constitute a complete physical picture: The lower energy ions absorb the wave energy, and thus get accelerated to higher energy. We use a nonadiabatic model to interpret the ion energy flux variations. Both analytic and simulation results are in good agreement with the observations. This indicates that the nonadiabatic acceleration associated with ULF waves superposed on dipolarized magnetic field is an effective mechanism for ion energization in the near-Earth plasma sheet. The presented energy flux structures can be used as a proxy to identify the similar dynamic process.

Nonadiabatic Tapered Optical Fiber for Biosensor Applications

A brief review on biconical tapered fiber sensors for biosensing applications is presented. A variety of configurations and formats of this sensor have been devised for label free biosensing based on measuring small refractive index changes. The biconical nonadiabatic tapered optical fiber offers a number of favorable properties for optical sensing, which have been exploited in several biosensing applications, including cell, protein, and DNA sensors. The types of these sensors present a low-cost fiber biosensor featuring a miniature sensing probe, label-free direct detection, and high sensitivity.