Coulomb Corrections Research Articles

Coulomb Corrections in Photoelectron Spectra in the Adiabatic Limit

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Multiphoton ionization of atoms in two-color laser field and coherent polarization control of terahertz waves

Within the framework of the Keldysh theory, the multiphoton ionization of atoms subjected to a perturbation by a high intensity two-color laser radiation field of an arbitrary polarization is considered. The dependence of the net photoelectron current, generated due to the interaction of an intense elliptically polarized two-color laser field with an atom, on the ratio of the second and fundamental harmonic amplitudes, their relative phase, and an angle between harmonics is found. The parameters maximizing the net photoelectron current are specified. Properties of polarization and spectral intensity of terahertz radiation and also possibility of the coherent control of terahertz waves polarization through the relative phase between harmonics in a two-color scheme are investigated. Using the ‘imaginary-time’ method, extremal subbarrier trajectories of the photoelectron moving in an elliptically polarized two-color laser field and the Coulomb correction to the total ionization rate are derived and discussed. The asymptotic expressions for the total ionization rate and the net photoelectron current obtained in the paper for the qualitative explanation of experiments on the generation of terahertz radiation in gases can be used.

Numerical tests of theoretical models describing ionization of H(1s) atom by linearly polarized flat pulse of laser radiation**Project supported by the University of Łódź.

We derive the well-known Coulomb correction factor for the Gordon–Volkov wave function describing an outgoing electron in the process of ionization in an intense laser field. Although rigorous treatment would limit its use only to laser fields much lower than the so-called barrier-suppression field, it appears that in practice the correction factor may be used also close to and even above this critical value of the laser field. We compare predictions of several analytical expressions describing ionization rate of the hydrogen atom in its ground state in the strong linearly polarized laser field. We also compare ionization probabilities obtained by integrating these ionization rates over a temporal envelope of the laser pulse with predictions based on the exact numerical solution to the time-dependent Schrödinger equation.

Ethane oxidative dehydrogenation mechanism on MoO3(010) surface: A first-principle study using on-site Coulomb correction

We applied the PBE+U method to investigate the mechanism of ethane oxidative dehydrogenation reaction (ODH) on the MoO3(010) surface. Our systematic study shows that ethylene generation is energetically a favorable pathway from the horizontal C2H6 adsorption. The vertical adsorption of C2H6 leads to the aldehyde generation along the α-oxidative dehydrogenation pathway (α-ODH). However, along the β-ODH pathway, the ethylene oxide formation is identified as the final product but may transform to produce ethylene from the CH2CH2O intermediate. The formation energy of oxygen vacancy (ΔEfv) of all types of oxygen atoms of the MoO3(010) surface are characterized with the on-site Coulomb correction, being reasonably consistent with the HSE results. The U correction leads to the mismatching between the dz2 orbital of Mo and pz orbitals of the terminal oxygen and consequently weakens the Mo–O chemical bond. Therefore, the weakened Mo–O chemical bond can increase the possibility of forming the oxygenated species, such as aldehyde and ethylene oxide.

Shock compression of strongly correlated oxides: A liquid-regime equation of state for cerium(IV) oxide

The shock Hugoniot for full-density and porous ${\mathrm{CeO}}_{2}$ was investigated in the liquid regime using ab initio molecular dynamics (AIMD) simulations with Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled by carrying out NVT simulations for isotherms between 6000 and 100 000 K and densities ranging from $\ensuremath{\rho}=2.5$ to $20\phantom{\rule{0.28em}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$. The impact of on-site Coulomb interaction corrections $+U$ on the equation of state (EOS) obtained from AIMD simulations was assessed by direct comparison with results from standard density functional theory simulations. Classical molecular dynamics (CMD) simulations were also performed to model atomic-scale shock compression of larger porous ${\mathrm{CeO}}_{2}$ models. Results from AIMD and CMD compression simulations compare favorably with Z-machine shock data to 525 GPa and gas-gun data to 109 GPa for porous ${\mathrm{CeO}}_{2}$ samples. Using results from AIMD simulations, an accurate liquid-regime Mie-Gr\"uneisen EOS was built for ${\mathrm{CeO}}_{2}$. In addition, a revised multiphase SESAME-type EOS was constrained using AIMD results and experimental data generated in this work. This study demonstrates the necessity of acquiring data in the porous regime to increase the reliability of existing analytical EOS models.

Integrated Cross Sections of High-Energy e+e– Pair Electroproduction by an Electron in an Atomic Field

The integrated cross sections of e+e– pair electroproduction by an ultrarelativistic electron in an atomic field are studied. The importance of various contributions to the integrated cross sections is discussed. The Coulomb corrections have turned out to make a large contribution to both differential and integrated cross sections even at moderate values of the nuclear charge number. The interaction of the electron emitting a virtual photon with the atomic field is shown to contribute significantly to the cross sections differential with respect to the electron transverse momentum. However, this interaction affects only slightly the cross section differential only with respect to the positron transverse momentum.

Soft-gluon and Coulomb corrections to hadronic top-quark pair production beyond NNLO

We construct a resummation at partial next-to-next-to-next-to-leading logarithmic accuracy for hadronic top-quark pair production near partonic threshold, including simultaneously soft-gluon and Coulomb corrections, and use this result to obtain approximate next-to-next-to-next-to-leading order predictions for the total top-quark pair-production cross section at the LHC. We generalize a required one-loop potential in non-relativistic QCD to the colour-octet case and estimate the remaining unknown twoloop potentials and three-loop anomalous dimensions. We obtain a moderate correction of 1.5% relative to the next-to-next-to-leading order prediction and observe a reduction of the perturbative uncertainty below ±5%.

Mechanistic Analysis of Oxygen Vacancy-Driven Conductive Filament Formation in Resistive Random Access Memory Metal/NiO/Metal Structures.

Electrically switchable resistive random access memories have drawn much interest as nonvolatile memory device candidates based on metal-insulator-metal (MIM) structure concepts. However, atomic level mechanisms that lead to conductive filament (CF) formation in MIM structures are often lacking, such as for the system with NiO as the oxide layer, which was found promising for resistive random access memory (RRAM) device applications. In this work, using density functional theory with a Hubbard-type on-site Coulomb correction, which we carefully benchmarked, we analyzed the intrinsic propensity toward CF formation in NiO upon introduction of oxygen vacancies, including interfacial effects of Ag or Pt electrodes. First, for stoichiometric MIM structural models, contributions from metal-induced gap states to the electronic density of states (DOS) were identified, accommodating oxygen vacancy states and showing that the interface region is reduced more easily than the bulklike region, for example, for the Ag/NiO/Ag structure. Moreover, a tendency toward oxygen vacancy clustering was demonstrated, important for CF formation. Indeed, by introducing ordered oxygen vacancies into the oxide layer for both MIM models, several extended defect states within the forbidden gap have resulted, which lead to defect-assisted transport. These were shown to be influenced by the spatial distribution and number of oxygen vacancies in the filament, where the degree of reduction of Ni atoms changes based on the immediate surroundings. Projected electronic DOS for individual Ni atoms in regions near and away from oxygen vacancies indicated that those Ni close to oxygen vacancies contribute most to the conductivity. Interestingly, based on charge analyses, these atoms are revealed to undergo significant reduction, generating a locally conductive region in the oxide layer that consists of metallic/near-metallic Ni (Ni0), formed through local reduction.

First principle calculations of structural, electronic and magnetic properties of cubic GdCrO3 Perovskite

The structural, electronic and magnetic properties of the cubic GdCrO3 perovskite are investigated by mean the full-potential linearized augmented plane wave method based on the density functional theory. We have used three approximations: the generalized gradient (GGA), the GGA + U, where U is on-site Coulomb interaction correction, and the modified Becke–Johnson (mBJ-GGA). Calculated Lattice parameters are where found to be in a very good agreement with experimental measurements. Our results of spin-polarized band structure and density of states show a metallic character of GdCrO3 when using the GGA scheme, whereas a half-metallic ferromagnetic behavior is observed in both cases of GGA + U and mBJ-GGA approaches with an important total magnetic moment of 10.00 μB. The obtained results show that GdCrO3 is an excellent candidate to spintronic applications.

High-energy μ+μ− electroproduction

The cross sections of high-energy μ+μ− pair production and paradimuonium production by a relativistic electron in the atomic field are discussed. The calculation is performed exactly in the parameters of the atomic field. Though the Coulomb corrections to the cross sections, related to the multiple Coulomb exchange of μ+,μ− and an atom, are negligible, the Coulomb corrections to the differential cross sections, related to the electron interaction with an atom, are large. However, the latter Coulomb corrections to the cross sections integrated over the final electron momentum are small. Apparently, this effect can easily be observed experimentally. Furthermore, it is shown that the asymmetry of the cross section with respect to the permutation of the momenta of μ− and μ+ is large.

Coulomb corrections to inclusive cross sections at the future Electron-Ion Collider

The experimental results of the future Electron-Ion ($eA$) Collider are expected to constrain the dynamics of the strong interactions at small values of the Bjorken $x$ variable and large nuclei. Recently it has been suggested that Coulomb corrections can be important in inclusive and diffractive $eA$ interactions. In this paper, we present a detailed investigation of the impact of the Coulomb corrections to some of the observables that will be measured in the future $eA$ collider. In particular, we estimate the magnitude of these corrections for the charm and longitudinal cross sections in inclusive and diffractive interactions. Our results demonstrate that the Coulomb corrections for these observables are negligible, which implies that they can be used to probe the QCD dynamics.

CO oxidation on inverse Ce6O12/Cu(111) catalyst: role of copper-ceria interactions.

The surface structures, O2 adsorption, and CO oxidation reaction properties of Ce6O12/Cu(111) have been investigated using density functional theory including on-site Coulomb corrections (DFT + U). Results show that the supported ceria nanoparticles would gain electrons from the Cu(111) surface, and the Ce4+ are reduced to Ce3+. In addition, the oxygens at the interface have been largely activated, resulting in much low formation energy of O vacancies. For the CO oxidation reaction, two possible pathways are investigated, CO reacts with the O2 molecule adsorbed on Ce3+ and the lattice O at the interface, respectively. It has been found that CO reacting with the lattice O atom gives a lower reaction barrier than that of adsorbed O2 on Ce3+. These results are important for further understanding of the role of different active sites on the inverse CeOx/Cu(111) surface structure.

Experimental investigation of strong-field-ionization theories for laser fields from visible to midinfrared frequencies

Ionization of atoms in intense laser fields is experimentally studied to evaluate the validity of the widely used ionization rate formulas from the ADK and PPT models at different laser wavelengths, intensities, polarizations and types of targets. It is found that the PPT model including the Coulomb correction agrees well with all the experimental data in the study, whereas the ADK formula can only be applied in some limited regimes.

Strong Correlation Effect in Ferrimagnetic Half-Metallic V2CoAl and V2CoGa Heusler Compounds

We present first-principles calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method to investigate the structural, elastic, electronic, and magnetic properties of the Heusler compounds V2CoAl and V2CoGa. We explore different magnetic configurations in both regular and inverse Heusler structures: the Cu2MnAl-type and Hg2CuTi-type structures respectively. Our compounds are found to be ferrimagnets in the inverse Heusler structure. To take into account the effects of the strong correlation among the localized d-states, we perform a calculation using the GGA+U method (the general gradient approximation with the Hubbard on-site Coulomb correction U). Then we show that both compounds exhibit a half-metallic character and have a magnetic moment of 2.00 μB per formula unit. This latter statement is coherent with the generalized Slater-Pauling rule (SP). In terms of the band structure calculations, we explain the formation of the indirect energy band gaps in the spin-majority channels. We also use the mean-field approximation (MFA) to discuss the magnetic exchange couplings and predict the Curie temperature for both compounds.

D + t → n + α fusion reaction in a model inspired by halo/cluster effective field theory

We study the low-energy [Formula: see text] fusion reaction using a model inspired by the halo/cluster effective field theory (H/CEFT) formalism. For this purpose, we initially focus on the [Formula: see text] reaction without considering the Coulomb force in the incoming deuteron–triton system. In the next step, we insert the Coulomb correction in the [Formula: see text] cross-section. The cross-section results involve unknown parameters. So, finally, we fit the H/CEFT cross-section of the [Formula: see text] reaction to the experimental data and obtain the values of these unknown parameters.

DFT + U and ab initio atomistic thermodynamics approache for mixed transitional metallic oxides: A case study of CoCu2O3 surface terminations

This study develops a systematic density functional theory alongside on-site Coulomb interaction correction (DFT + U) and ab initio atomistic thermodynamics approachs for ternary (or mixed transitional metal oxides), expressed in three reservoirs. As a case study, among notable multiple metal oxides, synthesized CoCu2O3 exhibits favourable properties towards applications in solar, thermal and catalytic processes. This progressive contribution applies DFT + U and atomistic thermodynamic approaches to examine the structure and relative stability of CoCu2O3 surfaces. Twenty-five surfaces along the [001], [010], [100], [011], [101], [110] and [111] low-Miller-indices, with varying surface-termination configurations were selected in this study. The results portray satisfactory geometrical parameters for bulk CoCu2O3, and a band gap of 1.25 e V. Furthermore, we clarified the stoichiometrically balanced inverted (010)CoCuO, and the non-stoichiometric (001)CuOCu, (001)CoOCo, (110)OCoO and (110)CoOCu surface terminations as the most stable configurations, out of which, the (001)CuOCu shows the optimum stability in ambient conditions. The systematic approach applied in this study should prove instrumental for the analysis of other 3-element multicomponent systems. To the best of our knowledge, the present study is the first to report DFT + U analysis to any 3-multicompnent systems with two of them requires inclusion of U treatment (i.e., f- and d- orbitals) in the electronic structure calculations.

Effects of Hubbard term correction on the structural parameters and electronic properties of wurtzite ZnO

The effects of including the Hubbard on-site Coulombic correction to the structural parameters and valence energy states of wurtzite ZnO were explored. Due to the changes in the structural parameters caused by correction of hybridization between Zn d states and O p states, suitable parameters of Hubbard terms have to be determined for an accurate prediction of ZnO properties. Using the LDA+U method by applying Hubbard corrections Ud to Zn 3d states and Up to O 2p states, the lattice constants were underestimated for all tested Hubbard parameters. The combination of both Ud and Up correction terms managed to widen the band gap of wurtzite ZnO to the experimental value. Pairs of Ud and Up parameters with the correct positioning of d-band and accurate bandwidths were selected, in addition to predicting an accurate band gap value. Inspection of vibrational properties, however, revealed mismatches between the estimated gamma phonon frequencies and experimental values. The selection of Hubbard terms based on electronic band properties alone cannot ensure an accurate vibrational description in LDA+U calculation.

Including Delbrück scattering in GEANT4

Elastic scattering of γ-rays is a significant interaction among γ-ray interactions with matter. Therefore, the planning of experiments involving measurements of γ-rays using Monte Carlo simulations usually includes elastic scattering. However, current simulation tools do not provide a complete picture of elastic scattering. The majority of these tools assume Rayleigh scattering is the primary contributor to elastic scattering and neglect other elastic scattering processes, such as nuclear Thomson and Delbrück scattering.Here, we develop a tabulation-based method to simulate elastic scattering in one of the most common open-source Monte Carlo simulation toolkits, GEANT4. We collectively include three processes, Rayleigh scattering, nuclear Thomson scattering, and Delbrück scattering. Our simulation more appropriately uses differential cross sections based on the second-order scattering matrix instead of current data, which are based on the form factor approximation. Moreover, the superposition of these processes is carefully taken into account emphasizing the complex nature of the scattering amplitudes. The simulation covers an energy range of 0.01MeV≤E≤3MeV and all elements with atomic numbers of 1≤Z≤99.In addition, we validated our simulation by comparing the differential cross sections measured in earlier experiments with those extracted from the simulations. We find that the simulations are in good agreement with the experimental measurements. Differences between the experiments and the simulations are 21% for uranium, 24% for lead, 3% for tantalum, and 8% for cerium at 2.754MeV. Coulomb corrections to the Delbrück amplitudes may account for the relatively large differences that appear at higher Z values.

Multifragmentation model for the production of astrophysical strangelets

Determination of baryon number (or mass) distribution of the strangelets, that may fragment out of the warm and excited strange quark matter ejected in the merger of strange stars in compact binary stellar systems in the Galaxy, is attempted here by using a statistical disassembly model. Finite mass of strange quarks is taken into account in the analysis. Resulting charges of the strangelets and the corresponding Coulomb corrections are included to get a plausible size distribution of those strangelets as they are produced in binary stellar mergers thus getting injected in the Galaxy. From this mass distribution of strangelets at their source, an approximate order of magnitude estimate for their possible flux in solar neighborhood is attempted by using a simple diffusion model for their propagation in the Galaxy. Such theoretical estimate is important in view of the ongoing efforts to detect galactic strangelets by recent satellite-borne experiments.

Strong-field ionization via a high-order Coulomb-corrected strong-field approximation

Signatures of the Coulomb corrections in the photoelectron momentum distribution during laser-induced ionization of atoms or ions in tunneling and multiphoton regimes are investigated analytically in the case of an one-dimensional problem. High-order Coulomb corrected strong-field approximation is applied, where the exact continuum state in the S-matrix is approximated by the eikonal Coulomb-Volkov state including the second-order corrections to the eikonal. Although, without high-order corrections our theory coincides with the known analytical R-matrix (ARM) theory, we propose a simplified procedure for the matrix element derivation. Rather than matching the eikonal Coulomb-Volkov wave function with the bound state as in the ARM-theory to remove the Coulomb singularity, we calculate the matrix element via the saddle-point integration method as by time as well as by coordinate, and in this way avoiding the Coulomb singularity. The momentum shift in the photoelectron momentum distribution with respect to the ARM-theory due to high-order corrections is analyzed for tunneling and multiphoton regimes. The relation of the quantum corrections to the tunneling delay time is discussed