Atomic Structure Calculations Research Articles

Identification of EUV spectral profiles of laser-produced Cr plasmas

SynopsisLaser-produced chromium (Cr) plasmas have been measured by using a temporal-spatially resolved laser-produced plasma emission spectroscopy technique. The emission peaks in the wavelength range of 6.5-15 nm were identified from the 3p-4d, 5d, and 3p-4s transition lines from Cr5+ to Cr10+ ions with aid of Cowan and Flexible Atomic Code (FAC) atomic structure calculations, and through comparative analysis between experimental and simulated spectra.

Bayesian atomic structure calculations for collisional problems

SynopsisThe calculations of collisional processes require an accurate description of the target. In general, the atomic structure is obtained through tedious iterations in which a variety of configurations and parameters are chosen to minimize the differences between the numerical and experimental values of the energies and the oscillator strengths. Using a Bayesian machine learning analysis through a Tree–structured Parzen Estimator, we can reproduce the experimental atomic structure with high accuracy. Results for neutral beryllium are presented.

Investigation of temporal-resolved spectra of laser-produced titanium plasmas

SynopsisLaser-produced titanium (Ti) plasmas have been measured using temporal-spatially resolved laser-produced plasma emission spectroscopy technique. The emission peaks in the wavelength range of 7.5-15 nm were identified from the 3s-(4,5)p, 3p-4d, and 3d-4f transition lines from Ti5+ to Ti11+ ions with aid of NIST database and Cowan atomic structure calculations, as well as comparative analysis between experimental and simulated spectra based on a simplified radiation hydrodynamic model.

Soft x-ray emission from laser-produced strontium ions

Soft x-ray spectra, in the range from 2 nm to 9 nm, were recorded from strontium plasmas formed by pulses from 20 ps, 170 ps and 5.5 ns Nd:YAG lasers operating at the fundamental wavelength of 1064 nm. Features due to 3d–4p and 3d–4f transitions were identified by comparison with spectra from adjacent ions and atomic structure calculations with both the Cowan code and the Flexible Atomic Code. As in the spectra of ions of other elements in the fifth row of the periodic table, resonant lines 3dn–3dn−14p1, 3dn–3dn−14f1 and satellite lines 3dn−14s1–3dn−24s14p1, 3dn−14s1–3dn−24s14f1 of Δn = 1 were observed over the 3.0–8.5 nm region, emitted by 10+ to 19+ ions. These Δn = 1 transitions provide a range of narrow band emission features which may match to specific multi layer combinations for reflective optics in the extreme ultraviolet region of the spectrum.

Spectral characterization of an industrial EUV light source for nanolithography

The emission spectra from an industrial, droplet-based, laser-produced plasma, extreme ultraviolet light source for nanolithography are here presented and analyzed. The dependence of spectral features on the CO2-drive-laser intensity is studied by changing the beam spot size at constant pulse energy and duration. We characterize the spectrum by fitting the results of atomic structure calculations to the short-wavelength region (7–11 nm), where the contributions from various charge states can be resolved, and obtain the relative contributions of charge states Sn9+ –Sn15+ . These relative contributions are compared to charge state populations as calculated with the non-equilibrium plasma kinetics code flychk. The calculations are shown to be in good qualitative agreement with the results, showing that the effective plasma temperature, and with it, the shape of the unresolved, main emission feature at 13.5 nm, is a remarkably weak function of laser intensity under this source normal operating conditions.

Isotope-shift spectroscopy of the 1 S 0 → 3 P 1 and 1 S 0 → 3 P 0 transitions in strontium.

Isotope-shift spectroscopy with narrow optical transitions provides a benchmark for atomic structure calculations and has also been proposed as a way to constrain theories predicting physics beyond the standard model. Here we measure frequency shifts of the 1 S 0 → 3 P 1 and 1 S 0 → 3 P 0 transitions between 84Sr,86Sr, and 87Sr, relative to 88Sr. Using the isotope-shift measurements of the two transitions, a King plot analysis is performed, revealing a nonlinearity in the measured values.

Population of the states in collisions of mixed‐state (1s21S,1s2s3S) B3+ and C4+ ion beams with He and H2 targets

Auger KLn lines are observed in high‐resolution electron spectra obtained in collisions of mixed‐state (1s21S,1s2s3S) He‐like beams of 4 MeV B3+ with H2 and 6 MeV C4+ with He targets. Supporting atomic structure calculations show these lines to correspond to doubly excited states, which can be readily populated by electron transfer to the component of the mixed‐state beam. They thus provide indirect evidence for the existence of the corresponding KLn quartet states, similarly produced, even though their weak Auger decay does not allow for their direct observation in the electron spectra. These KLn quartet states mostly decay in a cascade chain of strong radiative E1 transitions, eventually terminating at the state, which is thus additionally enhanced. An upper limit on the state population due to cascades is obtained by assuming a statistical production of KLn quartet to doublet states followed by a 100% cascade feeding of the state. Our estimated upper limit is supported by our absolute cross section measurements and corresponding three‐electron atomic orbital close coupling calculations in progress. Results to date are presented and discussed.

Energies, electric dipole (E1), quadrupole (E2), octupole (E3) and magnetic dipole (M1), quadrupole (M2) transition rates for Ca XII, Ti XIV, Cr XVI, Fe XVIII and Ni XX

Energies, weighted oscillator strengths (gf), line strengths (S) and radiative rates (A) for allowed and forbidden transitions are presented for 2s2p62S1/2 − 2s22p52P1/2, 2P3/2 and 2s22p52P1/2 − 2s22p52P3/2 transitions in fluorine-like Ca XII (Z = 20), Ti XIV (Z = 22), Cr XVI (Z = 24), Fe XVIII (Z = 26) and Ni XX (Z = 28) ions. Moreover, the allowed electric dipole (E1) and the forbidden electric quadrupole (E2), octupole (E3), magnetic dipole (M1) and quadrupole (M2) transition rates for some transitions are obtained. The 2s22p5–2s 2p6-type transitions of F-like ions are prominent in high-temperature plasmas and are useful for diagnostics. The present results are obtained from configuration interaction atomic structure calculations using the code SUPERSTRUCTURE (SS) which includes relativistic effects in Breit–Pauli approximation. The comparison of the present energies with the available observed energies displayed very good agreement (< 1%). The presented excitation energy results have been compared with other detailed relativistic approaches such as Dirac–Fock, coupled cluster and configuration interaction for a few ionic states.

Lifetime measurements of ultrashort‐lived excited states in Be‐like ions

We propose to measure the lifetime of short‐lived excited states in highly charged ions by pump‐probe experiments. Utilizing two synchronized and delayed Femtosecond pulses allows accessing these lifetimes with Femtosecond precision. Such measurements could provide sensitive tests of state‐of‐the art atomic structure calculations beyond the capabilities of established methods.

K‐line X‐ray fluorescence from highly charged iron ions under dense astrophysical plasma conditions

In the present work, we report an investigation of plasma environment effects on the atomic parameters associated with the K‐vacancy states in highly charged iron ions within the astrophysical context of accretion disks around black holes. More particularly, the sensitivity of K‐line X‐ray fluorescence parameters (wavelengths, radiative transition probabilities, and Auger rates) in Fe XVII–Fe XXV ions has been estimated for plasma conditions characterized by an electron temperature ranging from 105 to 107 K and an electron density ranging from 1018 to 1022 cm−3. In order to do this, relativistic multiconfiguration Dirac‐Fock atomic structure calculations have been carried out by considering a time averaged Debye‐Hückel potential for both the electron–nucleus and electron–electron interactions.

Relativistic atomic structure calculations of heavy targets for inelastic collisions

Fully relativistic atomic structure calculations for Zr, Nb, Pd, Gd, Er, Hf, Ta, Os, and Pt are presented here. The description of these atoms requires the solution of the Dirac equation. The electron binding energies attained are compared with experimental values, achieving excellent overall agreement for the inner shells. Discrepancies in the outer shell binding energies between the isolated atom and the solid are discussed, giving special attention to the open 4f–subshell. Based on the present calculations, we analyzed the valence shell of the nine elements studied here and propose theoretical values for the Wigner-Seitz radio.

Ambit: A programme for high-precision relativistic atomic structure calculations

We present the ambit software package for general atomic structure calculations. This software implements particle–hole configuration interaction with many-body perturbation theory (CI+MBPT) for fully relativistic calculations of atomic energy levels, electric- and magnetic-multipole transition matrix elements, g-factors and isotope shifts. New numerical methods and modern high-performance computing techniques employed by this software allow for the calculation of open-shell systems with many valence-electrons (N≥5) to a high degree of accuracy and in a highly computationally efficient manner. Program summaryProgram Title:ambitProgram Files doi:http://dx.doi.org/10.17632/7xfxhr9mg6.1Licensing provisions: GPLv3Programming language: C++11Nature of problem: Calculation of atomic/ionic spectra, including energy levels, electric and magnetic multipole transition matrix elements, and isotope shifts.Solution method: The programme calculates energy levels and wavefunctions using either configuration interaction (CI) only, or CI with many-body perturbation theory (CI+MBPT) in the Brillouin–Wigner MBPT formalism.Restrictions: The programme is not designed to treat highly-excited (Rydberg) states or continuum processes to a high degree of accuracy.Additional comments: Programme github repository

Pressure-Induced Band Structure Evolution of Halide Perovskites: A First-Principles Atomic and Electronic Structure Study

Density functional theory (DFT) based calculations have been conducted to draw a broad picture of pressure induced band structure evolution in various phases of organic and inorganic halide perovskite materials. Under a wide range of pressure applied, distinct band structure behaviors including magnitude change of band gap, direct-indirect/indirect-direct band gap transitions and CBM/VBM shifts, have been observed between organic and inorganic perovskites among different phases. Through atomic and electronic structure calculations, band gap narrowing/widening has been rationalized through crystal orbitals coupling transformations; direct-indirect mutual transitions were explained based on structural symmetry evolution; different VBM/CBM shifts behaviors between organic and inorganic perovskites were analyzed focusing on orientation and polarity of molecules/atoms outside the octahedrals. These results provide a comprehensive guidance for further experimental investigations on pressure engineering of perovskite materials.

Coercivity enhancement and magnetic property evaluation of Bi doped Mn2Sb

Abstract Mn2Sb is a well-known ferrimagnetic material, which has been investigated thoroughly to understand the effect of doping on its magnetic properties. Present work reports the synthesis of Bi doped Mn2Sb employing arc-melting and melt spinning followed by characterization with a view to establish a correlation in the structure and magnetic properties. Bi doping in Mn2Sb lattice produces a significant change in the latter’s magnetic properties, giving rise to a saturation magnetization of 27.2 emu/g (27.2 Am2/Kg) and a high coercivity value of 3.4 kOe (279.2 kA/m), in comparison to Mn2Sb, which has a coercivity of 0.1 kOe (7.96 kA/m). Theoretical studies were carried out to understand the changes in magnetic properties. Ab-initio electronic and atomic structure calculations show that Bi atom occupies equally the MnI and MnII sites and this leads to ferromagnetic ordering, which results in enhancement of the saturation magnetisation. The coercivity mechanism has also been studied in detail; the large coercivity is attributed to the nucleation mechanism achieved via the inclusion of diamagnetic Bi particles in Mn2Sb.

Spectroscopic diagnostics of low-ionized iron-peak elements. Electron-impact excitation of Ni3+ and photoionization of Ni2+

The spectra from Fe-peak elements may be used to determine the temperature and density of various astrophysical objects. Determination of these quantities is underpinned by the accuracy and the comprehensiveness of the underlying atomic structure and collisional calculations. In the following paper, we shall focus specifically on Ni IV lines associated with transitions amongst several low-lying levels. We shall employ modified versions of the parallel Dirac R-matrix codes, considering both electron-impact excitation of Ni$^{3+}$ and the photoionisation of both the ground and excited states of Ni$^{2+}$. We produce high-quality data sets for both processes, and using these data, we calculate line ratios relevant for plasma diagnostics of temperature and density.

First Principles Simulations on Migration Paths of Oxygen Interstitials in MgAl2O4

Thermal stability of the primary electronic defects – F‐type centers – in oxide materials is controlled by their recombination with much more mobile complementary defects – interstitial oxygen ions Oi. Thus, the study of interstitial ion migration is of key importance for the prediction of radiation damage in oxides. In this study, several possible migration trajectories for neutral and charged interstitial oxygen ions are calculated in MgAl2O4 spinel using the first principles calculations of atomic and electronic structure. The lowest energy barriers are ≈1.0–1.1 eV and 0.8 eV, respectively. The effective atomic charges, charge redistribution, and lengths of bonds closest to Oi interstitials are analyzed in detail.

Saturated-configuration-interaction calculations for five-valent Ta and Db

Accurate atomic structure calculations of complicated atoms with 4 or more valence electrons begin to push the memory and time limits of supercomputers. This paper presents a robust method of decreasing the size of \textit{ab initio} configuration interaction and many-body perturbation theory calculations without undermining the accuracy of the resulting atomic spectra. Our method makes it possible to saturate the CI matrix in atoms with many valence electrons. We test our method on the five-valence-electron atom tantalum and verify the convergence of the calculated energies. We then apply the method to calculate spectra and isotope shifts of tantalum's superheavy analogue dubnium. Isotope-shift calculations can be used to predict the spectra of superheavy isotopes which may be produced in astrophysical phenomena.

Extended atomic structure calculations for energy levels and radiative data of Xe XLIII

We report an extensive and elaborate theoretical study of atomic data for Xe XLIII. We have calculated energies for the lowest 141 fin. structure levels by using Multi-Configuration Dirac Fock (MCDF) method. We have also considered Quantum Electrodynamics (QED) and Breit corrections in our calculations. We have presented the radiative data for electric dipole (E1) transitions among lowest 141 levels. We have made comparisons of our calculated excitation energies and EUV (Extreme Ultraviolet) transition wavelengths with the theoretically computed and experimentally observed energy levels and wavelengths at Electron Beam Ion Trap (EBIT) and a good agreement is achieved. We have also computed energy levels by performing similar relativistic distorted wave calculations using Flexible Atomic Code (FAC). Additionally, we have provided new atomic data for Xe XLIII which are not published elsewhere in the literature. We believe that our results may be beneficial in fusion plasma research and detection and investigation of EUV and Soft X-ray (SXR) spectral lines.

5.96 keV Enerjide Hg, Pb and Bi Elementlerine ait Bileşiklerin Ortalama M Kabuğu Floresans Verimlerinin Araştırılması ve 70Yb ile 92U Arasındaki Elementlerin Ortalama M Kabuğu Floresans Verimlerinin Deneysel Olarak Hesaplanması

In this study, the empirical average M shell fluorescence yields were calculated from 70Yb to 92U. These obtained values will supply more experimental data for theoretical estimations of atomic structure calculations and spectroscopic analysis which is used for material characterization. And also, chemical effects on average M-shell fluorescence yields for Hg, Pb, and Bi compounds were determined using M X-ray production cross-sections at 5.96 keV photon energy. The samples were irradiated using a 1.85 GBq 55Fe radioactive source. M X-rays emitted by samples were counted using a multi-channel analyzer with a Ultra-LEGe detector. The measured experimental values have been compared with theoretically and empirically (only for M-shell average fluorescence yields) calculated values of pure elements.

Breit and QED Effects in Spectra of the 4s2 1S0−4s4p 3P1,1P1 Transitions in the Zn Sequence

The 4s2–4s4p E1 transitions for Zn-like ions from Z in the range 30–92 are calculated using the multiconfi guration Dirac–Hartree–Fock (MCDHF) method. The results obtained are in good agreement with other theoretical and experimental data and demonstrate the applicability of this method to high-precision atomic structure calculations of both few-electron systems and large atomic systems, such as Zn-like ions, along the entire isoelectronic sequence. We also report herein the calculations of many-electron quantum electrodynamic (QED) and Breit effects for the 3P0, 3P1, 3P2, and 1P1 states for all Zn-like ions in the range 30 ≤ Z ≤ 100.