Multielectron Effects Research Articles

Beyond the random phase approximation (RPA): First principles calculation of the valence EELS spectrum for KBr including local field, quasiparticle, excitonic and spin orbit coupling effects

The low energy region (< 50 eV) of the electron energy loss spectrum (EELS) can contain a great deal of spectral detail associated with excitations of the valence electrons. Calculation of the spectra from first principles can assist with interpretation and the most widely used method is the random phase approximation (RPA), usually neglecting local field effects (LFE). For KBr this approach is insufficient due to the importance of quasiparticle and excitonic effects. Calculations including these multi-electron effects are shown to give much improved agreement with the experimental spectra, and the inclusion of spin-orbit coupling (SOC) reproduces the excitonic doublet just above band-edge onset. A review of the complex theory behind these methods is given along with practical guidance on performing these calculations.

Precision spectroscopy on 9Be overcomes limitations from nuclear structure

Many powerful tests of the standard model of particle physics and searches for new physics with precision atomic spectroscopy are hindered by our lack of knowledge of nuclear properties. Ideally, these properties may be derived from precise measurements of the most sensitive and theoretically best-understood observables, often found in hydrogen-like systems. Although these measurements are abundant for the electric properties of nuclei, they are scarce for the magnetic properties, and precise experimental results are limited to the lightest of nuclei1–4. Here we focus on 9Be, which offers the unique possibility to use comparisons between different charge states available for high-precision spectroscopy in Penning traps to test theoretical calculations typically obscured by nuclear structure. In particular, we perform high-precision spectroscopy of the 1s hyperfine and Zeeman structure in hydrogen-like 9Be3+. We determine the effective Zemach radius with an uncertainty of 500 ppm, and the bare nuclear magnetic moment with an uncertainty of 0.6 parts per billion— uncertainties unmatched beyond hydrogen. Moreover, we compare our measurements with the measurements conducted on the three-electron charge state 9Be+ (ref. 5), which enables testing the calculation of multi-electron diamagnetic shielding effects of the nuclear magnetic moment at the parts per billion level. Furthermore, we test the quantum electrodynamics methods used for the calculation of the hyperfine splitting. Our results serve as a crucial benchmark for transferring high-precision results of nuclear magnetic properties across different electronic configurations.

Li2O–V2O5–MoO3–Fe2O3 amorphous cathode material for lithium-ion batteries based on coordinated multi-electron effect and stable network structure

The amorphous cathode materials Li2O–V2O5–MoO3 and Li2O–V2O5–MoO3–Fe2O3 were produced via melt quenching. By analyzing the structure, elemental valence, and electrochemical characteristics of Li2O–V2O5–MoO3 at different ratios, the effects of MoO3 addition on vanadium-based amorphous cathode materials were explored. 20Li2O–60V2O5–20MoO3 has a high initial capacity (268.0 mAh/g for the first reversible discharge at a current density of 50 mA/g), which is based on the properties that MoO3 supplies additional oxidation reductions and has [MoO6] structural units to widen the diffusion channels for lithium ions in the network structure. Unfortunately, the network of the structural elements [MoO6] and [VO4] is unstable, which causes the material to have poor cycle stability and exhibit an unsatisfactory current response. The network structure stability of Li2O–V2O5–MoO3–Fe2O3 is increased by adding Fe2O3 to provide [FeO4], which strengthens the link between each structural unit. Vanadium oxidation reductions are promoted, and iron oxidation reductions replace the role of molybdenum in the charge/discharge. The discharge product transforms from LiVMoO5 to Li2FeV3O8 with increased de-embedding Li efficiency. The 20Li2O–60V2O5–10MoO3–10Fe2O3 achieves an initial reversible specific capacity of 255.2 mAh/g at 50 mA/g, 139.7 mAh/g additional specific capacity after 100 cycles, and 110.5 mAh/g specific capacity at a high current density of 400 mA/g. The test findings show that 20Li2O–60V2O5–10MoO3–10Fe2O3 efficiently increases high-current responsiveness and cycle stability while retaining a high capacity. In this study, we propose a compositional design strategy, which is based on the coordinated multi-electronic effect of multiple transition metal elements and the design of a stable disordered network structure, to incorporate MoO3 and Fe2O3 into vanadium-based amorphous to create a novel cathode material. This work offers a fresh perspective on investigating innovative lithium-ion battery cathode materials.

Multielectronic and multiatomic effects in the U O4,5 x-ray absorption spectroscopy of uranium dioxide

In order to explain all of the spectral features observed in the U O4,5 x-ray absorption spectrum of uranium dioxide (UO2), it is necessary to include both multielectron effects and multiatomic effects. The 5d (core hole)-5f (electron) angular momentum coupling that gives rise to the giant resonance has been treated within ligand field density functional theory, and the electron scattering that generates the extended x-ray absorption fine structure has been included via the spectral simulation program FEFF: both within a UO8 fluorite cluster picture. An atomic model is insufficient to explain all of the observed spectral features.

Minimum structure of high-order harmonic spectrum from molecular multi-orbital effects involving inner-shell orbitals.

The spectral features of high-order harmonic spectra can provide rich information for probing the structure and dynamics of molecules in intense laser fields. We theoretically study the high harmonic spectrum with the laser polarization direction perpendicular to the N2O molecule and find a minimum structure in the plateau region of the harmonic spectrum. Through analyzing the time-dependent survival probability of different electronic orbitals and the time-dependent wave packet evolution, it is found that this minimum position is caused by the harmonic interference of HOMO a, HOMO-1, and HOMO-3 a orbitals. Moreover, this interference minimum is discovered over a wide frequency range of 0.087a.u. to 0.093a.u., as well as a range of driving laser intensities with peak amplitudes between 0.056 a.u. and 0.059 a.u.. This study sheds light on the multi-electron effects and ultrafast dynamics of inner-shell electrons in intense laser pulses, which are crucial for understanding and controlling chemical reactions in molecules.

High-order harmonic generation in the water window from mid-IR laser sources

We investigate the harmonic response of neon atoms to mid-IR laser fields ($2000--3000$ nm) using a single active electron (SAE) model and the fully ab initio all-electron $R$ matrix with time dependence (RMT) method. The laser peak intensity and wavelength are varied to find suitable parameters for high-harmonic imaging in the water window. Comparison of the SAE and RMT results shows qualitative agreement between them as well as parameters such as the cutoff frequency predicted by the classical three-step model. However, there are significant differences in the details, particularly in the predicted conversion efficiency. These details indicate the possible importance of multielectron effects, as well as a strong sensitivity of quantitative predictions on specific aspects of the numerical model.

Calculation of high-order harmonic generation of atoms and molecules by combining time series prediction and neural networks.

High-order harmonic generation (HHG) from the interaction of ultra-intense laser pulses with atoms is an important tabletop short-wave coherent light source. Accurate quantum simulations of it present large computational difficulties due to multi-electron multidimensional effects. In this paper, the time-dependent response of hydrogen atoms is calculated using a time-series prediction scheme, the HHG spectrum is reconstructed very accurately. The accuracy of the forecasting is further improved by using a neural network scheme. This scheme is also applied to the simulation of the harmonic emission on multi-electron systems, and the applicability of the scheme is confirmed by the harmonic calculation of complex systems. This method is expected to simulate the nonlinear dynamic process of multi-electron atoms and molecules irradiated by intense laser pulses quickly and accurately.

Multielectron effects in CO ionization by orthogonal two-color laser fields

We study the single ionization of CO molecule in orthogonally polarized two-color laser fields using time-dependent Hartree–Fock method. Employing the coherent superposition consisting of a fundamental field and its second harmonic, we consider different wavelengths (780 and 390nm) and intensities (1×1014, 1.5×1014 and 2×1014 W/cm2) of the fundamental field for which different ionization mechanisms are involved. Our numerical results reveal that the contributions of the three highest occupied molecular orbitals are strongly influenced by the intensity ratio and time delay between the two components of the bichromatic field. At the fundamental wavelength of 780nm and intensity of 2×1014 W/cm2, the two outermost molecular orbitals display a dominant response to the orthogonal two-color laser field when the second harmonic field is stronger than the fundamental field.

Multielectron effect in XUV light-driven strong-field ionization beyond the dipole approximation

By applying the time-dependent density-functional theory, we theoretically investigate the multielectron effect in the extreme UV (XUV) light-driven ionization of atoms and diatomic molecules beyond the dipole approximation. Compared to the theoretical results obtained in the single active electron approximation, the multielectron effect leads to more tilted photoelectron angular momentum distributions (PADs) toward the light propagation direction. According to our analysis, this might be due to photon momentum sharing between multiple electrons. Furthermore, we study the multielectron effect on the birth time delay phenomenon in the ionization of a hydrogen molecule. By extracting the interference minima of the PADs, we demonstrate that the birth time delay is hardly affected by the multielectron effect. The present work provides a better understanding of the association between the nondipole effect and the multielectron effect.

Resonance absorption of the inner shell during high-order harmonic generation.

In this work, we report the observation of resonance absorption of the inner shell during the high-order harmonic generation (HHG) from xenon (Xe) and krypton (Kr). The absorption peaks show a periodic variation with the change of carrier-envelope phase of driving laser pulses and the delay of two-color laser field, which indicates the absorption peaks come from the collective multielectron effects during the HHG. With the increase of gas pressure, the depth of absorption peak will continue to increase, while due to the phase matching effect, there will be an optimal pressure for the intensity of harmonic signal. Our experimental results pave the way to uncover the physical mechanism of the collective multielectron effects involving inner-shell electrons in the HHG process.

Asymmetry in high-order harmonic generation of polar molecule CO

Compared with nonpolar molecules, owing to the inherent asymmetry, polar molecules exhibit rich and very complex electronic dynamics under the interaction with strong laser fields. In this work, high-order harmonic generation (HHG) of polar molecules CO is investigated by using the three-dimensional time-dependent Hartree-Fock (3D-TDHF) theory, with all electrons active. Through the high harmonic spectra and time-frequency analyses, it is found that when the laser field polarizes along the molecular axis, the ionized electrons from the two sides (C side and O side) contribute differently to the harmonic radiation. On the one hand, the harmonic intensity from the C side is greater than that from the O side, which is caused by the ionization rate. On the other hand, for the lower-order (7&lt;sup&gt;th&lt;/sup&gt;–17&lt;sup&gt;th&lt;/sup&gt; order) harmonics of plateau region, only the electrons from the C side participate in the HHG. However, for its higher part (18&lt;sup&gt;th&lt;/sup&gt;–36&lt;sup&gt;th&lt;/sup&gt; order), the electrons from both C side and O side contribute to high harmonics simultaneously. Moreover, the difference between contributions from two sides is related to the alignment angle &lt;i&gt;θ&lt;/i&gt; between the laser polarization and the molecular axis, and it reaches a maximum value around &lt;i&gt;θ&lt;/i&gt; = 0º and a minimum value around &lt;i&gt;θ&lt;/i&gt; = 90º. There are two strong resonances around harmonic order H12.6 (19.5 eV) and H18 (27.9 eV) in the harmonic spectra when &lt;i&gt;θ&lt;/i&gt; = 0º. The first resonance around H12.6 reveals that part of electrons ionized from the C side recombine to the vicinity of the further O nucleus. Near the second resonance around H18, there appears a shape resonance. Nevertheless, the shape resonances from the C and O sides are disparate. Based on the strong-field approximation theory, the ratio between photoionization cross sections from C and O sides around the shape resonance is calculated. The ratio is about 5.5 from 3D-TDHF, which is greater than the result of 3 simulated by ePloyScat, where only HOMO is considered. This discrepancy reveals that multi-electron effects enhance the asymmetry of polar molecules. This work provides an in-depth insight into the asymmetry in HHG of polar molecules, which benefits the generation of isolated attosecond pulse . It also promotes the application of high harmonic spectra in tracking the ultrafast dynamics of electrons.

Nondipole effects on the double-slit interference in molecular ionization by xuv pulses.

The double-slit interference in single-photon ionization of the diatomic molecular ion H2 + is theoretically studied beyond the dipole approximation. Via simulating and comparing the interactions of the prealigned H2 + and the hydrogen atom with the xuv pulses propagating in different directions, we illustrate two kinds of effects that are encoded in the interference patterns of the photoelectrons from H2 +: the single-atom nondipole effect and the two-center-interference one, both associated with the finite speed of light. While the two effects could modify the maxima of the interference fringes, we show that the former one hardly affects the interference minima. Our results and analysis show that the interference minima rule out the influences of the photon-momentum transfer and, potentially, the multielectron effect, thus performing a better role in decoding the zeptosecond time delay for the pulse hitting one and the other atomic centers of the molecule.

Three-dimensional tomographic imaging of CO molecular orbitals reveals multi-electron effects

According to the asymmetric molecular orbital reconstruction algorithm, which divides orbital into gerade and ungerade components and which does not depend on the unidirectional recollisional condition, we obtain the two-dimensional highest occupied molecular orbital (HOMO) of CO based on the directly calculated transition dipole moment and the harmonic spectra calculated by the Lewenstein model, respectively, which is the three-dimensional (3D) HOMO projected onto the plane perpendicular to the laser propagation direction. In order to retrieve the full orbital function, a 3D molecular orbital tomography (MOT) method is developed and is successfully applied to the reconstructions of the HOMO of CO, which simplifies the 3D imaging process of orbitals of linear molecules, and is expected to be extended to reconstruct the 3D orbitals of nonlinear molecules. In addition, the time-dependent density functional theory is employed to acquire the harmonic spectra of CO in a 800 nm and 1500 nm wavelength laser, respectively. The comparison of these two reconstruction results helps identify the multi-electron effects for asymmetric MOT, which requires further study. This work advances the development of MOT and is expected to reveal multi-electron effects in orbital imaging of complex polyatomic molecules.

Multielectron effects in strong-field ionization of the oriented OCS molecule

We present theoretical calculations of orientation-dependent total ionization yields from the highest occupied molecular orbitals of the oriented OCS molecule by solving the time-dependent Schr\"odinger equation in three dimensions. The calculations were performed within the single-active-electron approximation including multielectron polarization. The multielectron polarization term was represented by an induced dipole term which contains the polarizability of the OCS + cation parallel to the laser polarization. Upon accounting for multielectron polarization, the calculated total ionization yields and their orientation dependence are in good agreement with experimental data.

Photodetachment spectroscopy of quasibound states of the negative ion of lanthanum

The negative ion of lanthanum, La$^-$, has one of the richest bound state spectra observed for an atomic negative ion and has been proposed as a promising candidate for laser-cooling applications. In the present experiments, La$^-$ was investigated using tunable infrared photodetachment spectroscopy. The relative signal for neutral atom production was measured with a crossed ion-beam--laser-beam apparatus over the photon energy range 590 - 920 meV (2100 - 1350 nm) to probe the continuum region above the La neutral atom ground state. Eleven prominent peaks were observed in the La$^-$ photodetachment cross section due to resonant excitation of quasibound transient negative ion states in the continuum which subsequently autodetach. In addition, thresholds were observed for photodetachment from several bound states of La$^-$ to both ground and excited states of La. The present results provide information on the excited state structure and dynamics of La$^-$ that depend crucially on multielectron correlation effects.

Static-field ionization model of He-like ions for diagnostics of light-field intensity

We study static-field ionization of He-like ions with nuclear charge number in the range of $2\le Z \le 36$. Both the tunneling and over-the-barrier regimes are considered. We calculate the ionization rates by three approximate methods: a fitting formula based on the Perelemov-Popov-Terent'ev (PPT) formula, a perturbative expansion in powers of $1/Z$, and a single-active electron approximation, and compare them with reference ionization rates computed by the multiconfiguration time-dependent Hartree-Fock (MCTDHF) approach. The relative deviation of the rates computed by the PPT-based fitting formula and the third-order perturbation theory from the rates computed by the MCTDHF approach is found to be around 10\%. We discuss quantitatively the contribution from the exchange interaction during the ionization by comparing the single-active electron rates and the reference rates in which multielectron effects are included. We find that a single-active electron approximation, where the exchange interaction is neglected, results in the overestimation of the ionization rates by 30\% for He and 2\% for He-like Kr, showing that the magnitude of the effect of the exchange interaction scales approximately as $1/Z$.

Multielectron Effect for High-Order Harmonic Generation From Molecule Irradiated by Bichromatic Counter-Rotating Circularly Polarized Laser Pulses

We investigated high-order harmonic generation in molecules N2 and C6H6 irradiated by bichromatic counter-rotating circularly polarized laser pulses by using time-dependent density-functional theory methods. It is found that $3N$ ( $N$ is an integer) order harmonics in C6H6 disappear. Whereas, $N$ order harmonics are obtained in N2. Analysis of the high harmonic generated from individual electronic orbital of the molecule, shows that, the characteristics of harmonic spectra are determined by the spatial distribution of electronic orbits. Moreover, effects of molecular orientation on harmonic emission are also presented.

Nonadiabatic and Multielectron Effects in the Attoclock Experimental Scheme* *Supported by the National Key Research and Development Program of China (Nos. 2019YFA0307700 and 2016YFA0401100), the National Natural Science Foundation of China (Nos. 11527807, 11774387, 11834015, 11847243, 11804374, 11874392, and 11974383), the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB21010400), and the Science and Technology Department of

The problem of how long it takes for an electron to tunnel from one side of a barrier to the other has been debated for decades and the attoclock is a promising experimental procedure to address this problem. In the attoclock experiment, many physical effects will contribute to the experimental results and it is difficult to extract the tunneling time accurately. We numerically investigate a method of measuring the residual equivalent temporal offset (RETO) induced by the physical effects except for tunneling delay. The Coulomb potential effect, the nonadiabatic effect, the multielectron effect, and the Stark effect are considered in the theoretical model. It is shown that the ratio of the RETO of the target atoms to that of H is insensitive to the wavelength and is linearly proportional to . This work can help to improve the accuracy of the attoclock technique.

Strong effect of multi-electron oxygen reduction reaction on photocatalysis through the promotion of interfacial charge transfer

An efficient visible-light-driven photocatalyst with interface charge transfer (IFCT) effect was achieved by assembling Fe-porphyrin based conjugated microporous polymer on TiO2 microspheres. It was revealed that IFCT effect played a crucial role in the enhancement of photocatalytic performance. In addition, the oxygen reduction reaction (ORR) activity of TiO2 was enhanced in the presence of Fe-porphyrin based conjugated microporous polymer and IFCT effect was promoted obviously due to the high ORR activity. It’s speculated that multi-electron ORR could accelerate the consumption of photoinduced electrons, retarding the recombination of photoinduced holes and electrons in the IFCT process, leaving more high-oxidizing photoinduced holes in the valance band of TiO2 for further degradation. What’s more, to further clarify the relationship between multi-electron ORR and IFCT effect, the influence of electron transfer number on the generation of photoinduced holes in the IFCT process was studied, and it was believable that four-electron oxygen reduction process was better able to accelerate the generation of photoinduced holes in the IFCT process than two-electron oxygen reduction process, resulting in higher photocatalytic activity.

Electronic wavefunctions probed by all-optical attosecond interferometry

Photoelectron spectroscopy is a powerful method that provides insight into the quantum mechanical properties of a wide range of systems. The ionized electron wavefunction carries information on the structure of the bound orbital, the ionic potential as well as the photo-ionization dynamics itself. While photoelectron spectroscopy resolves the absolute amplitude of the wavefunction, retrieving the spectral phase information has been a long-standing challenge. Here, we transfer the electron phase retrieval problem into an optical one by measuring the time-reversed process of photo-ionization -- photo-recombination -- in attosecond pulse generation. We demonstrate all-optical interferometry of two independent phase-locked attosecond light sources. This measurement enables us to directly determine the phase shift associated with electron scattering in simple quantum systems such as helium and neon, over a large energy range. In addition, the strong-field nature of attosecond pulse generation resolves the dipole phase around the Cooper minimum in argon through a single scattering angle, along with phase signatures of multi-electron effects. Our study bears the prospect of probing complex orbital phases in molecular systems as well as electron correlations through resonances subject to strong laser fields.