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The influence of plasma screening on the excitation energies and transition properties of He-like Ni26+ ion under strongly coupled plasma background has been analyzed. To perform the analysis, the multi-configuration Dirac–Fock method has been adopted by incorporating the ion sphere model potential as a modified interaction potential between the electron and the nucleus. For comparison purposes, parallel calculations have been carried out using the modified relativistic configuration interaction method. It is found that the transition energies corresponding to principal quantum number conserving transitions (Δn = 0) are blue shifted, whereas they are redshifted for the transitions where the principal quantum number is not conserved (Δn ≠ 0). The variation of transition probabilities and weighted oscillator strengths with free electron densities has also been studied. The present results should be advantageous in the modeling and diagnostics of astrophysical and laboratory plasmas.

An extended calculation of energy levels, radiative rates, and lifetimes are reported for sodium-like chromium. Extensive configuration interaction calculations have been performed using general-purpose relativistic atomic structure package (GRASP). The radiative rates, oscillator strengths, and line strengths are listed for all electric dipole (E1) transitions. However, for magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions, only radiative rates are listed. The importance of valence–valence (VV) and core–valence (CV) correlation effects in the calculation of energy levels have also been shown. To confirm the accuracy of the present results for energy levels by GRASP, independent calculations have been performed by using Flexible Atomic Code (FAC) and configuration interaction method (CIV3). The accuracy of the present levels, wavelengths, transition rates, and lifetimes are assessed by comparing them to available experimental and other theoretical results. We believe that our extensive results may be beneficial in fusion plasma research and astrophysical investigations and applications.

Electron impact excitation collision strengths for the transitions among the lowest twelve fine structure levels belonging to $$2\hbox {p}^{\mathrm {6}}\hbox {nl }$$ ( $$\hbox {\textit{n}}=3,4,\hbox {\textit{l}}=0-3$$ ) configurations of Cu XIX ion are presented using the close-coupling Breit–Pauli R-matrix method. Target state wavefunctions have been constructed using the AUTOSTRUCTURE. The collision strengths are also tabulated at selected energies above the excitation thresholds in the range 50–300 Ryd. For assessing the accuracy and reliability of our collision strength values, an independent calculation has been carried out using the relativistic distorted wave method. The effective collision strengths are obtained over a wide electron temperature range of $$1.0\times 10^{\mathrm {5}} - 4.0\times 10^{\mathrm {7}}$$ K by averaging over a Maxwellian distribution of velocities. We believe that our present results will be beneficial in the modelling of astrophysical and fusion plasmas.

Extensive and elaborate theoretical computations of Cu XIX have been performed by employing multi-configuration Dirac-Fock (MCDF) method. We have presented energy levels and radiative data such as, transition wavelengths, radiative rates, oscillator strengths and line strengths for electric dipole (E1) transitions in Na-like Cu. For other types of transitions, namely magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2), only the A-values are listed. We have also discussed the importance and the effect of valence-valence (VV) and core-valence (CV) correlations on the excitation energies in graphical as well as in tabular form. The accuracies of the presented levels, wavelengths, transition rates and lifetimes are assessed by comparing them to available experimental and other theoretical results. Analogous calculations have been carried out by using Flexible Atomic Code (FAC) based on self-consistent Dirac-Fock-Slater iteration method. QED corrections due to vacuum polarization and self-energy effects, and Breit correction due to the exchange of virtual photons between two electrons are fully considered and their effects on the energy levels are studied graphically. The fine-structure energy levels have also been reported by using the Configuration Interaction (CIV3) technique. An intercomparison among three independent calculations helps us in assessing the credibility and integrity of our reported data. Additionally, we have shown the variation of the line intensity ratios and electron density with plasma temperature graphically for Cu XIX. We have also identified Extreme Ultraviolet (EUV) and Soft X-ray (SXR) transitions and believe that our reported results may be beneficial in space and laboratory plasma research.

Extensive and systematic calculations for energy levels and lifetimes are carried out for the lowest 145 levels arising from the 3s23p4, 3s3p5, 3s23p33d, 3p6, 3s3p43d and 3s23p23 d2 configurations in S-like Kr XXI ion using the multiconfiguration Dirac-Fock (MCDF) method. Additionally, radiative data such as transition wavelengths, absorption oscillator strengths, line strengths and radiative decay rates have also been computed for electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1) and magnetic quadrupole (M2) transitions from the ground state. The importance of Breit interaction (BI) and quantum electrodynamics (QED) corrections on the energy levels has also been estimated. To assess the credibility and integrity of our MCDF energies, independent calculations using the relativistic configuration interaction (RCI) approach have also been performed. Detailed comparisons are made between our two sets of results, as well as with other existing experimental and theoretical values, and a good agreement is achieved. The present results will be helpful for the modeling and diagnostics of fusion plasmas.

The effect of strongly coupled plasma environment on the photoionization cross sections of the H-like O7+ ion is studied within the framework of relativistic configuration interaction technique implemented in the flexible atomic code. The analytical b-potential of Li and Rosmej [Phys. Lett. A 384, 126478 (2020)] and uniform electron gas model potential of Saha and Fritzsche [J. Phys. B 40, 259 (2007)] have been employed for incorporating the plasma shielding effects. The level energies for unscreened H-like O7+ ion are in excellent agreement with the National Institute of Standards and Technology values. The bound and continuum state wavefunctions are determined by solving the modified Dirac equations. The photoionization cross sections evaluated in the dipole approximation are obtained from the bound-free transition matrix element. Cross section calculations are performed over an electron density range of 1.0 × 1019–2.0 × 1023 cm−3 and a temperature range of 200–1000 eV. The plasma environment is found to considerably influence the photoionization cross sections. It has been observed that the ionization thresholds move to the low energy region with the increase in free electron densities. The present results will be beneficial for the interpretation of spectra observed in a variety of astrophysical and laboratory plasmas.

Plasma shielding effects on the energy levels and radiative properties of He-like Ca\(^{18+}\) ion under dense plasma conditions have been studied. For this purpose, the multiconfiguration Dirac-Fock method has been implemented by incorporating the ion sphere model potential as a modified interaction potential between the electron and the nucleus. To check the authenticity of our results, independent calculations have been performed using the modified relativistic configuration interaction method. It is observed that the transition energies associated with \(\Delta n = 0\) transitions are blue shifted, whereas red shifted for \(\Delta n \neq 0\) transitions. The variation in transition probabilities and weighted oscillator strengths with plasma densities has also been analyzed. The present results should be beneficial in the plasma modeling and fusion plasma research applications.

The total photoionization cross sections for the ground state 2p63s2(1S0) and the lowest three excited states 2p63s3p(3Po0,1,2) of the Mg-like Cu XVIII ion have been calculated by making use of the close-coupling Breit Pauli R-matrix (BPRM) approximation. The lowest 21 target level states of Cu XIX have been included in the photoionization calculations of Cu XVIII. Our calculated target state energies of the core ion Cu XIX show a good agreement with the observed energies tabulated in the NIST database. To further assess the accuracy of our BPRM results, photoionization cross section calculations for the ground state configuration have also been performed by employing the fully relativistic Dirac atomic R-matrix code (DARC). Our two independent calculations show a reasonable agreement between the calculated cross sections in the overall background shape and magnitude. We believe that our cross section data may be beneficial for the modelling and diagnostics of astrophysical and laboratory plasmas.

The influence of plasma screening on the transition energies and radiative properties of He-like ions embedded in dense plasma environment has been analyzed. For this purpose, the multiconfiguration Dirac-Fock method and Flexible Atomic Code incorporating the analytical plasma screening potential of Li et al. (2019) [39] and uniform electron gas model potential have been implemented. Our calculated line shifts of 1 s 2 S 0 1 → 1 s 3 p P 1 o 1 He-β transition of Cl15+ are in excellent agreement with the recent measurements of Beiersdorfer et al. (2019) [11] . The plasma shielding effects on 1 s 2 S 0 1 → 1 s n p P 1 o 3 ( n = 2 , 3 ) and 1 s 2 S 0 1 → 1 s n p P 1 o 1 ( n = 2 , 3 ) transitions of Ar16+, Ti20+ and Fe24+ ions have also been studied. It is found that transition energies for these transitions are red shifted with respect to free electron densities. The present results should be advantageous in the modeling and diagnostics of laboratory and astrophysical plasmas.

Photoionization cross sections of the ground state 2p63s2 (1S0) and the first three excited states 2p63s3p (3Po0,1,2) of Mg-like Se XXIII have been reported by employing the fully relativistic Dirac atomic R-matrix code (DARC). For construction of target wavefunctions, multiconfiguration Dirac-Fock calculations are performed for the lowest 21 fine structure energy levels belonging to 2p6nl (3 ≤ n ≤ 5) configurations. Our calculated target state energies of the core ion Se XXIV show close agreement with the energies tabulated in the NIST database. In order to assess the accuracy of our DARC results, photoionization cross section calculations of the ground state configuration have also been performed using the close-coupling Breit-Pauli R-matrix (BPRM) method. Our two independent calculations show a good agreement both in magnitude and resonant photoionization cross sections. The resonance energies (Er) and widths (Γ) of the 3pns (3P1,1P1), 3pnd (3D1, 3P1, 1P1), 3dnp (3D1, 3P1, 1P1) and 3dnf (3D1, 3P1, 1P1) series due to ejection of a 3s electron from the ground state 2p63s2 (1S0) have also been predicted by adopting Quigley and Berrington (QB) method. We believe that our results might be beneficial for the modelling and diagnostics of fusion and laser generated plasmas.

Extensive calculations of energy levels and radiative data such as transition wavelengths, radiative rates, oscillator strengths, and line strengths for electric dipole (E1) transitions have been performed for Se XXIV using the multiconfiguration Dirac–Fock method. For other types of transitions, namely, magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2), only the radiative rates (A) are listed. The importance and effect of valence-valence and core-valence correlations on the excitation energies have been studied. For additional accuracy assessments, analogous calculations have been carried out by employing the flexible atomic code and configuration interaction technique. Comparisons are made with the available experimental and theoretical data in the literature. Close agreement has been found ensuring the accuracy and reliability of our results. The effect of plasma temperature on the line intensity ratio, electron density, plasma frequency, and skin depth has been analyzed for hot dense plasma (HDP) in local thermodynamic equilibrium. The present work might be beneficial in the modeling and characterization of HDP.Extensive calculations of energy levels and radiative data such as transition wavelengths, radiative rates, oscillator strengths, and line strengths for electric dipole (E1) transitions have been performed for Se XXIV using the multiconfiguration Dirac–Fock method. For other types of transitions, namely, magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2), only the radiative rates (A) are listed. The importance and effect of valence-valence and core-valence correlations on the excitation energies have been studied. For additional accuracy assessments, analogous calculations have been carried out by employing the flexible atomic code and configuration interaction technique. Comparisons are made with the available experimental and theoretical data in the literature. Close agreement has been found ensuring the accuracy and reliability of our results. The effect of plasma temperature on the line intensity ratio, electron density, plasma frequency, and skin depth has been analyzed for ...