arXiv subjects

P. Jönsson

Publications and source records attributed to P. Jönsson.

At least 19 recordsLinked to original sources

arXiv2026

Accurate transition and hyperfine data in Ag I from Multiconfiguration Dirac-Hartree-Fock and Relativistic Coupled-Cluster methods

Silver is a key tracer of the weak r-process in late-type stars. However, when the assumption of local thermodynamic equilibrium (LTE) needs to be relaxed, accurate abundance determinations become even more sensitive to complete sets of reliable transition data. The aim of this work is to provide accurate and extensive results of excitation energies, radiative transition and hyperfine data for Ag I. The Multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic coupled-cluster (RCC) methods were used in the present work. The quantitative and qualitative evaluation (QQE) approach is applied to the MCDHF transition rates to estimate the uncertainty according to the National Institute of Science and Technology Atomic Spectroscopic Data (NIST ASD) terminology. Excitation energies, transition data and hyperfine structure constants were calculated for $18$ states up to $4d^{10}8s$. $57$ electric dipole (E1) transition rates and weighted oscillator strengths are computed and estimated to be in the following NIST ASD uncertainty classes; $4$ in AA, $12$ in A+, $5$ in A, $13$ in B+, $6$ in B, $4$ in C+ with AA $\leq 1\%$, A+ $\leq 2\%$, A $\leq 3\%$, B+ $\leq 7\%$, B $\leq 10\%$, C+ $\leq 18\%$. The remaining transitions, mainly weak transitions involving the $4d^95s^2$ states, are estimated to be in the E class $>50\%$. The computed lifetimes from both the MCDHF and RCC methods are in good mutual agreement and mostly fall within the error bars of available experimental values from laser induced fluorescence (LIF) measurements. The $4d^95s^2~^2D_{5/2}$ metastable state, important for establishing the ionization balance, decay through an E2 transition to the ground state. The calculated lifetime is $163\,\mathrm{ms}$. The computed hyperfine interaction constants from the MCDHF and RCC methods are in good agreement and compare well with the scattered experimental constants.

physics.atom-ph↗

arXiv2026

Theoretical investigation of transition data of astrophysical importance in neutral sulphur

Accurate and comprehensive atomic data are essential for the modelling of stellar spectra. Uncertainties in the oscillator strengths of specific lines used for abundance analyses directly translate into uncertainties in the derived elemental abundances; incomplete or biased atomic data sets can impart significant errors in non-local thermodynamic equilibrium (non-LTE) modelling. Theoretical calculations of atomic data are therefore crucial to supplement the limited experimental results. In this work, we present extensive atomic data, including oscillator strengths, transition rates, and lifetimes for 1730 electric-dipole (E1) transitions among 107 levels in neutral sulphur (S I) using the multi-configuration Dirac-Hartree-Fock (MCDHF) and relativistic-configuration-interaction (RCI) methods. These levels belong to the configurations $\mathrm{3p^3np (n=3-7)}$, $\mathrm{3p^3nf (n=4,5)}$, $\mathrm{3s3p^5}$, $\mathrm{3p^3ns (n=4-7)}$, and $\mathrm{3p^3nd (n=3-6)}$. The accuracy of the computed transition rates is assessed by combining the comparison of the differences in transition rates between the Babushkin and Coulomb gauges with a cancellation-factor (CF) analysis. Approximately 16% of the ab initio results achieved an accuracy classification of A-B, corresponding to uncertainties within 10%, as defined by the Atomic Spectra Database of the National Institute of Standards and Technology (NIST ASD). Applying a fine-tuning technique was found to significantly improve the accuracy of the results in the Coulomb gauge, thereby improving the consistency between the Babushkin and Coulomb gauges; about 24% of the fine-tuned transition data are assigned to the accuracy classes A-B.

physics.atom-ph↗

arXiv2023

Extended atomic data for oxygen abundance analyses

As the most abundant element in the universe after hydrogen and helium, oxygen plays a key role in planetary, stellar, and galactic astrophysics. Its abundance is especially influential on stellar structure and evolution, and as the dominant opacity contributor at the base of the Sun's convection zone it is central to the discussion around the solar modelling problem. However, abundance analyses require complete and reliable sets of atomic data. We present extensive atomic data for O I, by using the multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods. Lifetimes and transition probabilities for radiative electric dipole transitions are given and compared with results from previous calculations and available measurements. The accuracy of the computed transition rates is evaluated by the differences between the transition rates in Babushkin and Coulomb gauges, as well as by a cancellation factor analysis. Out of the 989 computed transitions in this work, 205 are assigned to the accuracy classes AA-B, that is, with uncertainties less than 10%, following the criteria defined by the National Institute of Standards and Technology Atomic Spectra Database. We discuss the influence of the new log(gf) values on the solar oxygen abundance and ultimately advocate $\logε_{\mathrm{O}}=8.70\pm0.04$.

astro-ph.SR↗

arXiv2023

Extended MCDHF calculations of energy levels and transition data for N I

Accurate and extensive atomic data are essential for spectroscopic analyses of stellar atmospheres and other astronomical objects. We present energy levels, lifetimes, and transition probabilities for neutral nitrogen, the sixth most abundant element in the cosmos. The calculations employ the fully relativistic multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, and span the 103 lowest states up to and including 2s$^2$2p$^2$5s. Our theoretical energies are in excellent agreement with the experimental data, with an average relative difference of 0.07%. In addition, our transition probabilities are in good agreement with available experimental and theoretical data. We further verify the agreement of our data with experimental results via a re-analysis of the solar nitrogen abundance, with the results from the Babushkin and Coulomb gauges consistent to 2% or 0.01 dex. We estimated the uncertainties of the computed transition data based on a statistical analysis of the differences between the transition rates in Babushkin and Coulomb gauges. Out of the 1701 computed electric dipole transitions in this work, 83 (536) are associated with uncertainties less than 5% (10%).

physics.atom-ph↗

arXiv2021

Extended theoretical transition data in C I - IV

Accurate atomic data are essential for opacity calculations and for abundance analyses of the Sun and other stars. The aim of this work is to provide accurate and extensive results of energy levels and transition data for C I - IV. The Multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods were used in the present work. To improve the quality of the wave functions and reduce the relative differences between length and velocity forms for transition data involving high Rydberg states, alternative computational strategies were employed by imposing restrictions on the electron substitutions when constructing the orbital basis for each atom and ion. Transition data, e.g., weighted oscillator strengths and transition probabilities, are given for radiative electric dipole (E1) transitions involving levels up to 1s$^2$2s$^2$2p6s for C I, up to 1s$^2$2s$^2$7f for C II, up to 1s$^2$2s7f for C III, and up to 1s$^2$8g for CIV. Using the difference between the transition rates in length and velocity gauges as an internal validation, the average uncertainties of all presented E1 transitions are estimated to be 8.05%, 7.20%, 1.77%, and 0.28%, respectively, for C I - IV. Extensive comparisons with available experimental and theoretical results are performed and good agreement is observed for most of the transitions. In addition, the C I data were employed in a reanalysis of the solar carbon abundance. The new transition data give a line-by-line dispersion similar to the one obtained when using transition data that are typically used in stellar spectroscopic applications today.

physics.atom-ph↗

arXiv2020

Extended Calculations with Spectroscopic Accuracy: Energy Levels and Radiative Rates for O-like Ions between Ar XI and Cr XVII

Using the multiconfiguration Dirac-Hartree-Fock and the relativistic configuration interaction methods, a consistent set of transition energies and radiative transition data for the main states of the $2s^2 2p^4$, $2s 2p^5$, $2p^6$, $2s^2 2p^3 3s$, $2s^2 2p^3 3p$, $2s^2 2p^3 3d$, $2s 2p^4 3s$, $2s 2p^4 3p$, and $2s 2p^4 3d$ configurations in O-like Ions between Ar XI ($Z = 18$) and Cr XVII ($Z = 24$) is provided. Our data set is compared with the NIST compiled values and previous calculations. The data are accurate enough for identification and deblending of new emission lines from hot astrophysical and laboratory plasmas. The amount of data of high accuracy is significantly increased for the $n = 3$ states of several O-like ions, where experimental data are very scarce.

physics.atom-ph↗

arXiv2020

Large-scale multiconfiguration Dirac-Hartree-Fock calculations for astrophysics: n=4 levels in P-like ions from Mn~XI to Ni~XIV

Using the multiconfiguration Dirac-Hartree-Fock and the relativistic configuration interaction methods, a consistent set of transition energies and radiative transition data for the lowest 546 (623, 701, 745) states of the $3p^4 3d$, $3s 3p^2 3d^2$, $3s 3p^3 4p$, $3s 3p^4$, $3s^2 3d^3$, $3s^2 3p^2 3d$, $3s^2 3p^2 4d$, $3s^2 3p^2 4s$, $3p^3 3d^2$, $3p^5$, $3s 3p 3d^3$, $3s 3p^3 3d$, $3s 3p^3 4s$, $3s^2 3p 3d^2$, %$3s^2 3p^2 4f$, $3s^2 3p^2 4p$, $3s^2 3p^3$ configurations in Mn~XI (Fe~XII, Co~XIII, Ni~XIV) is provided. The comparison between calculated excitation energies for the $n=4$ states and available experimental values for Fe XII indicate that the calculations are highly accurate, with uncertainties of only a few hundred cm$^{-1}$. Lines from these states are prominent in the soft X-rays. With the present calculations, several recent new identifications are confirmed. Other identifications involving $3p^2 4d$ levels in Fe~XII that were found questionable are discussed and a few new assignments are recommended. As some $n=4$ states of the other ions also show large discrepancies between experimental and calculated energies, we reassess their identification. The present study provides highly accurate atomic data for the $n=4$ states of P-like ions of astrophysical interest, for which experimental data are scarce.

physics.atom-ph↗

arXiv2019

Large-scale multiconfiguration Dirac-Hartree-Fock calculations for astrophysics: Cl-like ions from Cr~VIII to Zn~XIV

We use the multiconfiguration Dirac-Hartree-Fock (MCDHF) method combined with the relativistic configuration interaction (RCI) approach (GRASP2K) to provide a consistent set of transition energies and radiative transition data for the lower $n =3$ states in all Cl-like ions of astrophysical importance, from \ion{Cr}{8} to \ion{Zn}{14}. We also provide excitation energies calculated for \mbox{Fe X} using the many-body perturbation theory (MBPT, implemented within FAC). The comparison of the present MCDHF results with MBPT and with the available experimental energies indicates that the theoretical excitation energies are highly accurate, with uncertainties of only a few hundred cm$^{-1}$. Detailed comparisons for Fe~X and Ni~XII highlight discrepancies in the experimental energies found in the literature. Several new identifications are proposed.

physics.atom-ph↗

arXiv2018

Extended transition rates and lifetimes in Al I and Al II from systematic multiconfiguration calculations

Multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) calculations were performed for 28 and 78 states in neutral and singly ionized aluminium, respectively. In Al I, the configurations of interest are $3s^2nl$ for $n=3,4,5$ with $l=0$ to $4$, as well as $3s3p^2$ and $3s^26l$ for $l=0,1,2$. In Al II, the studied configurations are, besides the ground configuration $3s^2$, $3snl$ with $n=3$ to $6$ and $l=0$ to $5$, $3p^2$, $3s7s$, $3s7p$ and $3p3d$. Valence and core-valence electron correlation effects are systematically accounted for through large configuration state function (CSF) expansions. Calculated excitation energies are found to be in excellent agreement with experimental data from the NIST database. Lifetimes and transition data for radiative electric dipole (E1) transitions are given and compared with results from previous calculations and available measurements, for both Al I and Al II. The computed lifetimes of Al I are in very good agreement with the measured lifetimes in high-precision laser spectroscopy experiments. The present calculations provide a substantial amount of updated atomic data, including transition data in the infrared region. This is particularly important since the new generation of telescopes are designed for this region. There is a significant improvement in accuracy, in particular for the more complex system of neutral Al I. The complete tables of transition data are available.

physics.atom-ph↗

arXiv2018

Energy Levels, Lifetimes and Transition rates for P-like ions from Cr X to Zn XVI from large-scale Relativistic Multiconfiguration Calculations

The fully relativistic multiconfiguration Dirac--Hartree--Fock method is used to compute excitation energies and lifetimes for the 143 lowest states of the $3s^23p^3$, $3s3p^4$, $3s^23p^23d$, $3s3p^33d$, $3p^5$, $3s^23p3d^2$ configurations in P-like ions from Cr X to Zn XVI. Multipole (E1, M1, E2, M2) transition rates, line strengths, oscillator strengths, and branching fractions among these states are also given. Valence-valence and core-valence electron correlation effects are systematically accounted for using large basis function expansions. Computed excitation energies are compared with the NIST ASD and CHIANTI compiled values and previous calculations. The mean average absolute difference, removing obvious outliers, between computed and observed energies for the 41 lowest identified levels in Fe XII is only 0.057 \%, implying that the computed energies are accurate enough to aid identification of new emission lines from the sun and other astrophysical sources. The amount of energy and transition data of high accuracy is significantly increased for several P-like ions of astrophysics interest, where experimental data are still very scarce.

physics.atom-ph↗

arXiv2018

Extended calculations of energy levels, radiative properties, $A_{J}$, $B_{J}$ hyperfine interaction constants, and Landé $g_{J}$-factors for nitrogen-like \mbox{Ge XXVI}

Employing two state-of-the-art methods, multiconfiguration Dirac--Hartree--Fock and second-order many-body perturbation theory, highly accurate calculations are performed for the lowest 272 fine-structure levels arising from the $2s^{2} 2p^{3}$, $2s 2p^{4}$, $2p^{5}$, $2s^{2} 2p^{2} 3l$~($l=s,p,d$), $2s 2p^{3}3l$ ($l=s,p,d$), and $2p^{4} 3l$ ($l=s,p,d$) configurations in nitrogen-like Ge XXVI. Complete and consistent atomic data, including excitation energies, lifetimes, wavelengths, hyperfine structures, Landé $g_{J}$-factors, and E1, E2, M1, M2 line strengths, oscillator strengths, and transition rates among these 272 levels are provided. Comparisons are made between the present two data sets, as well as with other available experimental and theoretical values. The present data are accurate enough for identification and deblending of emission lines involving the $n=3$ levels, and are also useful for modeling and diagnosing fusion plasmas.

physics.atom-ph↗

arXiv2017

Extended Calculations of Spectroscopic Data: Energy Levels, Lifetimes and Transition rates for O-like ions from Cr XVII to Zn XXIII

Employing two state-of-the-art methods, multiconfiguration Dirac--Hartree--Fock and second-order many-body perturbation theory, the excitation energies and lifetimes for the lowest 200 states of the $2s^2 2p^4$, $2s 2p^5$, $2p^6$, $2s^2 2p^3 3s$, $2s^2 2p^3 3p$, $2s^2 2p^3 3d$, $2s 2p^4 3s$, $2s 2p^4 3p$, and $2s 2p^4 3d$ configurations, and multipole (electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2)) transition rates, line strengths, and oscillator strengths among these states are calculated for each O-like ion from Cr XVII to Zn XXIII. Our two data sets are compared with the NIST and CHIANTI compiled values, and previous calculations. The data are accurate enough for identification and deblending of new emission lines from the sun and other astrophysical sources. The amount of data of high accuracy is significantly increased for the $n = 3$ states of several O-like ions of astrophysics interest, where experimental data are very scarce.

physics.atom-ph↗

arXiv2016

Abundances of disk and bulge giants from hi-res optical spectra: I. O, Mg, Ca, and Ti in the Solar neighborhood and Kepler field samples

The galactic bulge is a significant part of our galaxy, but it is hard to observe, being both distant and covered by dust in the disk. Therefore there do not exist many hi-res optical spectra of bulge stars with large wavelength coverage, whose determined abundances can be compared with nearby, similarly analyzed stellar samples. We aim to determine the, for chemical evolution models, so important alpha elements of a sample of bulge giants using hi-res optical spectra with large wavelength coverage. The abundances found will be compared to similarly derived abundances from similar spectra of similar stars in the local thin and thick disks. In this first paper we focus on the Solar neighborhood reference sample. We use spectral synthesis to derive the stellar parameters as well as the elemental abundances of both the local as well as the bulge samples of giants. Special care is taken to benchmark our method of determining stellar parameters against independent measurements of effective temperatures from angular diameter measurements and surface gravities from asteroseismology. In this first paper we present the method used to determine the stellar parameters as well as the elemental abundances, evaluate them, and present the results for our local disk sample of 291 giants. When comparing our determined spectroscopic temperatures to those derived from angular diameter measurements, we reproduce these with a systematic difference of +10 K and a standard deviation of 53 K. The spectroscopic gravities are reproducing the ones determined from asteroseismology with a systematic offset of +0.10 dex and a standard deviation of 0.12 dex. When it comes to the abundance trends, our sample of local disk giants is closely following that of other works analyzing solar neighborhood dwarfs, showing that the much brighter giant stars are as good abundance probes as the often used dwarfs.

astro-ph.GA↗

arXiv2016

Calculations with spectroscopic accuracy: energies and transition rates in the nitrogen isoelectronic sequence from Ar XII to Zn XXIV

Combined relativistic configuration interaction and many-body perturbation calculations are performed for the 359 fine-structure levels of the $2s^2 2p^3$, $2s 2p^4$, $2p^5$, $2s^2 2p^2 3l$, $2s 2p^3 3l$, $2p^4 3l$, and $2s^2 2p^2 4l$ configurations in N-like ions from Ar XII to Zn XXIV. A complete and consistent data set of energies, wavelengths, radiative rates, oscillator strengths, and line strengths for all possible electric dipole, magnetic dipole, electric quadrupole, and magnetic quadrupole transitions among the 359 levels are given for each ion. The present work significantly increases the amount of accurate data for ions in the nitrogen-like sequence, and the accuracy of the energy levels is high enough to serve identification and interpretation of observed spectra involving the $n=3,4$ levels, for which the experimental values are largely scarce. Meanwhile, the results should be of great help in modeling and diagnosing astrophysical and fusion plasmas.

physics.atom-ph↗

arXiv2014

Hyperfine structures and Landé $g_J$-factors for $n=2$ states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations

Energy levels, hyperfine interaction constants, and Landé $g_J$-factors are reported for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations. Valence, core-valence, and core-core correlation effects are taken into account through single and double-excitations from multireference expansions to increasing sets of active orbitals. A systematic comparison of the calculated hyperfine interaction constants is made with values from the available literature.

physics.atom-ph↗

arXiv2014

Isotope Shifts in Beryllium-, Boron-, Carbon-, and Nitrogen-like Ions from Relativistic Configuration Interaction Calculations

Energy levels, normal and specific mass shift parameters as well as electronic densities at the nucleus are reported for numerous states along the beryllium, boron, carbon, and nitrogen isoelectronic sequences. Combined with nuclear data, these electronic parameters can be used to determine values of level and transition isotope shifts. The calculation of the electronic parameters is done using first-order perturbation theory with relativistic configuration interaction wave functions that account for valence, core-valence and core-core correlation effects as zero-order functions. Results are compared with experimental and other theoretical values, when available.

physics.atom-ph↗

arXiv2013

A Partitioned Correlation Function Interaction approach for describing electron correlation in atoms

Traditional multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) methods are based on a single orthonormal orbital basis (OB). For atoms with complicated shell structures, a large OB is needed to saturate all the electron correlation effects. The large OB leads to massive configuration state function (CSF) expansions that are difficult to handle. We show that it is possible to relax the orthonormality restriction on the OB and break down the originally large calculations to a set of smaller ones that can be run in parallel. Each calculation determines a partitioned correlation function (PCF) that accounts for a specific correlation effect. The PCFs are built on optimally localized orbital sets and are added to a zero-order multireference (MR) function to form a total wave function. The mixing coefficients of the PCFs are fixed from a small generalized eigenvalue problem. The required matrices are computed using a biorthonormal transformation technique. The new method, called partitioned correlation function interaction (PCFI), converges rapidly and gives total energies that are lower than the ordinary ones (MCHF and CI). Considering Li I, we show that by dedicating a PCF to the single excitations from the core highly improves the convergence patterns of the hyperfine parameters. Collecting the optimized PCFs to correct the MR function, the variational degrees of freedom in the relative mixing coefficients of the CSFs building the PCFs are inhibited. These constraints lead to small off-sets in computed properties other than total energy, with respect to the correct values. By (partially) deconstraining the mixing coefficients one converges to the correct limits and keeps the important advantage in the convergence rates. Reducing ultimately each PCF to a single CSF with its own OB leads to a non-orthogonal CI approach. Various perspectives of the new method are given.

physics.atom-ph↗

arXiv2011

Tensorial form and matrix elements of the relativistic nuclear recoil operator

Within the lowest-order relativistic approximation ($\sim v^2/c^2$) and to first order in $m_e/M$, the tensorial form of the relativistic corrections of the nuclear recoil Hamiltonian is derived, opening interesting perspectives for calculating isotope shifts in the multiconfiguration Dirac-Hartree-Fock framework. Their calculation is illustrated for selected Li-, B- and C-like ions. The present work underlines the fact that the relativistic corrections to the nuclear recoil are definitively necessary for getting reliable isotope shift values.

physics.atom-ph↗