Some of the to determine wavefunctions for atoms and ions, using both nonrelativistic and relativistic formulations, on the use of the generic configuration interaction for many-electron systems. Some of the of relativistic for transition energies and

The development of theoretical and computational atomic and molecular physics in the second half of the twentieth century owes a great deal to Phil Burke. His knowledge and insight, his enthusiasm and encouragement, his vision and determination were essential characteristics for the success of his work and that of many others. He developed and used the R-matrix method in the study of the interaction between, on the one hand, atoms and molecules and their ions and, on the other, light or electrons. He published many original research papers and was author or editor of a number of books. Especially significant and far-reaching was his setting up of the journal Computer Physics Communications to enable an international field of scientists, initially to share computer codes, but subsequently also to discuss and develop methods in computational physics. While based at the Daresbury Laboratory, he established a number of Collaborative Computational Projects, thus providing a forum for scientists working in specific scientific disciplines to meet periodically to discuss current issues and in particular how the ever advancing cutting-edge of high-end computing could begin to address previously intractable problems. A consequence was his clarity of thinking about which new computer architectures were needed to make significant advances in each field of study, expertly guiding the UK's provision of high-end computers to academia for over 20 years. He was a clear and methodical teacher, at both graduate and undergraduate level, and was generous with the time he gave to his students. In short, he demonstrated a balanced level of excellence in all aspects of his career. He was a consummate academic and a fine role model for his colleagues.

Inner-shell photodetachment of Na− near the L-edge threshold was investigated using the R-matrix method. Significant structure was found in the cross section, and this structure is shown to be related to the complicated correlated electron dynamics endemic in negative ions. Comparison with experiment suggests that the absolute values of the measured cross section might be too small by a factor of two.

Charlotte Froese Fischer has been at the forefront of research in atomic structure theory for over 60 years. She has developed many of the methods currently used by researchers and has written associated computer programs which have been published and hence made accessible to the research community. Throughout her career, she has consistently encouraged and mentored young scientists, enabling them to embark on independent careers of their own. This article provides an overview of the methods and codes she has developed, some large-scale calculations she has undertaken, and some insight into the impact she has had on young scientists, and the leadership she continues to show as she reaches her 90th birthday.

Absolute total, partial, and differential cross sections for the photodetachment of the oxygen anion are reported for photon energies ranging from threshold (1.46 eV) to 5.5 eV. The total cross section was measured using the animated-crossed-beam technique while partial and differential cross sections were obtained using velocity map imaging. The measured values are in good agreement with theoretical results obtained from an R-matrix calculation using polarized pseudostates.

There is an on-going need for accurate oscillator strengths to be used in astrophysical applications, particularly in plasma diagnostics and in the modelling of stellar atmospheres and the interstellar medium. There are several databases in regular use which contain some of the required data, although often insufficiently complete, and sometimes not sufficiently accurate. In addition, several atomic structure packages are available through the literature, or from their individual authors, which would allow further calculations to be undertaken. Laboratory measurements provide an important check on the accuracy of calculated data, and the combined efforts of theorists and experimentalists have succeeded in providing data of an accuracy sufficient for some astrophysical applications. However, the insufficiency or inadequacy of atomic data is a continuing problem. We discuss in the context of appropriate examples some of the principal steps which researchers have taken to calculate accurate oscillator strengths, including both ab initio results and also various extrapolation processes which attempt to improve such results. We also present some examples of the main causes of difficulty in such calculations, particularly for complex (many-electron) ions, and indicate ways in which the difficulties might be overcome.

Recent experimental work by Belmonte et al. (2014) has given rates for some 4p–4d transitions that are significantly at variance with the previous experimental work of Rudko and Tang (1967) recommended in the NIST tabulations. To date, there are no theoretical rates with which to compare. In this work, we provide such theoretical data. We have undertaken a substantial and systematic configuration interaction calculation, with an extrapolation process applied to ab initio mixing coefficients, which gives energy differences in agreement with experiment. The length and velocity forms give values that are within 10%–15% of each other. Our results are in sufficiently close agreement with those of Belmonte et al. that we can confidently recommend that their results are much more accurate than the early results of Rudko and Tang, and should be adopted in place of the latter.

Recent, state-of-the-art calculations of A-values and electron impact excitation rates for Fe III are used in conjunction with the Cloudy modeling code to derive emission-line intensity ratios for optical transitions among the fine-structure levels of the 3d(6) configuration. A comparison of these with high-resolution, high signal-to-noise spectra of gaseous nebulae reveals that previous discrepancies found between theory and observation are not fully resolved by the latest atomic data. Blending is ruled out as a likely cause of the discrepancies, because temperature- and density-independent ratios (arising from lines with common upper levels) match well with those predicted by theory. For a typical nebular plasma with electron temperature T-e = 9000 K and electron density N-e = 10(4) cm(-3) 3, cascading of electrons from the levels (3)G(5), (3)G(4) and (3)G(3) plays an important role in determining the populations of lower levels, such as F-3(4), which provide the density diagnostic emission lines of Fe III, such as D-5(4) - F-3(4) at 4658 angstrom. Hence, further work on the A-values for these transitions is recommended, ideally including measurements if possible. However, some Fe III ratios do provide reliable N-e-diagnostics, such as 4986/4658. The Fe III cooling function, calculated with Cloudy using the most recent atomic data, is found to be significantly greater at T-e similar or equal to 30,000 K than predicted with the existing Cloudy model. This is due to the presence of additional emission lines with the new data, particularly in the 1000-4000 angstrom wavelength region.

The generalized oscillator strengths (GOSs) of 2p(5)(3d,4s, 4d, 4f) states excited from neon ground state, are studied by the configuration interaction (C I) method and the random phase approximation with exchange (RPAE). Wavefunctions of these states obtained from the configuration interaction code CIV3 of Hibbert are employed to compute these GOSs. We report results of calculations for both the velocity and length formulations of the GOS for the neon transitions 2p(6) -> 2p(5)4s, 2p(6) -> 2p(5)(3d,4d) and 2p(6) 2p(5)4f respectively for multipole strengths l=1, l=1, 3 and l=2, 4 respectively. The results show remarkable agreement among the extrema positions resulting from the velocity and length forms despite the rather different absolute values of GOS they reveal. This work reduces significantly the difference between the extrema positions of the GOS obtained in the theoretical calculations of Amusia et al. and those experimentally found by Chen et al. for dipole 2p(6) -> 2p(5)4s transition. The profiles of our calculated GOS are in agreement with the theoretical results of Amusia et al. In the present work, for the 2p6 2p5(3d,4d) transitions, our length dipole RPAE GOS curves agree with the pictures obtained from the data RPAE GOS of Amusia et al. while the length octupole GOS have values smaller than those of the Amusia et al. GOS results except in the small squared transferred momentum K-2 region. Good agreement between our length RPAE GOS and the recent RPAE results of Amusia et al. is found for the quadrupole excitation to 2p54f. The results of length and velocity hexadecapole GOS are comparable with each other for the same transition, and experimental work is needed. The present calculations also reveal that the electron correlations effects are noticeable around the region of the GOS maxima. (C) 2017 Elsevier Ltd. All rights reserved.

Aims. We present rates for all E1, E2, M1, and M2 transitions among the 295 fine-structure levels of the configurations 3d(9), 3d(8)4s, 3d(7)4s(2), 3d(8)4p, and 3d(7)4s4p, determined through an extensive configuration interaction calculation.Methods. The CIV3 code developed by Hibbert and coworkers is used to determine for these levels contiguration interaction wave functions with relativistic effects introduced through the Breit-Pauli approximation.Results. Two different sets of calculations have been undertaken with different 3d and 4d functions to ascertain the effect of such variation. The main body of the text includes a representative selection of data, chosen so that key points can be discussed. Some analysis to assess the accuracy of the present data has been undertaken, including comparison with earlier calculations and the more limited range of experimental determinations. The full set of transition data is given in the supplementary material as it is very extensive.Conclusions. We believe that the present transition data are the best currently available.

Photoionization cross sections are obtained using the relativistic Dirac Atomic R-matrix Codes (DARC) for all valence and L-shell energy ranges between 27-270eV. A total of 557 levels arising from the dominant configurations 3s$^2$3p$^4$, 3s3p$^5$, 3p$^6$, 3s$^2$3p$^3$[3d, 4s, 4p], 3p$^5$3d, 3s$^2$3p$^2$3d$^2$, 3s3p$^4$3d, 3s3p$^3$3d$^2$ and 2s$^2$2p$^5$3s$^2$3p$^5$ have been included in the target wavefunction representation of the Ar III ion, including up to 4p in the orbital basis. We also performed a smaller Breit-Pauli (BP) calculation containing the lowest 124 levels. Direct comparisons are made with previous theoretical and experimental work for both valence shell and L-shell photoionization. Excellent agreement was found for transitions involving the $^2$P$^{\rm o}$ initial state to all allowed final states for both calculations across a range of photon energies. A number of resonant states have been identified to help analyze and explain the nature of the spectra at photon energies between 250 and 270eV.

Modelling of massive stars and supernovae (SNe) plays a crucial role in understanding galaxies. From this modelling we can derive fundamental constraints on stellar evolution, mass-loss processes, mixing, and the products of nucleosynthesis. Proper account must be taken of all important processes that populate and depopulate the levels (collisional excitation, de-excitation, ionization, recombination, photoionization, bound-bound processes). For the analysis of Type Ia SNe and core collapse SNe (Types Ib, Ic and II) Fe group elements are particularly important. Unfortunately little data is currently available and most noticeably absent are the photoionization cross-sections for the Fe-peaks which have high abundances in SNe. Important interactions for both photoionization and electron-impact excitation are calculated using the relativistic Dirac atomic R-matrix codes (DARC) for low-ionization stages of Cobalt. All results are calculated up to photon energies of 45 eV and electron energies up to 20 eV. The wavefunction representation of Co III has been generated using GRASP0 by including the dominant 3d(7), 3d(6)[4s, 4p], 3p(4)3d(9) and 3p(6)3d(9) configurations, resulting in 292 fine structure levels. Electron-impact collision strengths and Maxwellian averaged effective collision strengths across a wide range of astrophysically relevant temperatures are computed for Co III. In addition, statistically weighted level-resolved ground and metastable photoionization cross-sections are presented for Co II and compared directly with existing work.

In this work we explore the validity of employing a modified version of the nonrelativistic structure code CIV3 for heavy, highly charged systems, using Na-like tungsten as a simple benchmark. Consequently, we present radiative and subsequent collisional atomic data compared with corresponding results from a fully relativistic structure and collisional model. Our motivation for this line of study is to benchmark CIV3 against the relativistic GRASP(0) structure code. This is an important study as CIV3 wave functions in nonrelativistic R-matrix calculations are computationally less expensive than their Dirac counterparts. There are very few existing data for the WLXIV ion in the literature with which we can compare except for an incomplete set of energy levels available from the NIST database. The overall accuracy of the present results is thus determined by the comparison between the CIV3 and GRASP(0) structure codes alongside collisional atomic data computed by the R-matrix Breit-Pauli and Dirac codes. It is found that the electron-impact collision strengths and effective collision strengths computed by these differing methods are in good general agreement for the majority of the transitions considered, across a broad range of electron temperatures.

Astrophysics is driven by observations, and in the present era there are a wealth of state-of-the-art ground-based and satellite facilities. The astrophysical spectra emerging from these are of exceptional quality and quantity and cover a broad wavelength range. To meaningfully interpret these spectra, astronomers employ highly complex modelling codes to simulate the astrophysical observations. Important input to these codes include atomic data such as excitation rates, photoionization cross sections, oscillator strengths, transition probabilities and energy levels/line wavelengths. Due to the relatively low temperatures associated with many astrophysical plasmas, the accurate determination of electron-impact excitation rates in the low energy region is essential in generating a reliable spectral synthesis. Hence it is these atomic data, and the main computational methods used to evaluate them, which we focus on in this publication. We consider in particular the complicated open d- shell structures of the Fe-peak ions in low ionization stages. While some of these data can be obtained experimentally, they are usually of insufficient accuracy or limited to a small number of transitions.

In this paper we present photoionization cross sections for the lowest five states of O-like S IX (1s(2)2s(2)2p(4) P-3(0,1,2), D-1(2), S-1(0)). The relativistic Breit-Pauli R-matrix codes were utilized including all terms of the 2s(2)2p(3), 2s2p(4), 2p(5), 2s(2)2p(2)3s, 3p, 3d and 2s2p(3)3s, 3p, 3d configurations in the expansion of the collision wavefunction for S X. It was also found that to achieve convergence of the low-lying energy separations of the target levels, an additional 21 configuration functions needed to be included in the configuration interaction expansion, incorporating two-electron excitations from the 2s and 2p shells to the 3s, 3p and 3d shells. The present work thus constitutes the most sophisticated photoionization evaluation for ground and metastable levels of the S IX ion. Direct comparisons have been made with the only available data found on the OPEN-ADAS database between level resolved contributions of the spectrum. This comparison for the background cross section exhibits excellent agreement at all photon energies for each partial photoionization cross section contribution investigated. Finally, the autoionizing bound states arising from numerous open channels have also been investigated and identified using the QB approach, a procedure for analyzing resonances in atomic and molecular collision theory which exploits the analytic properties of R-matrix theory. Major Rydberg resonance series are also presented and tabulated for the dominant linewidths considered.

We have performed large-scale configuration interaction (CI) calculations using CIV3for the lowest (in energy) 155 fine-structure levels of aluminum-like germanium ion. We have calculated the energy levels, lifetimes, oscillator strengths, and transition probabilities for the electric-dipole allowed and intercombination transitions among the levels of ground state3s23p(2P)and higher energy levels of states3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2,3p3d2, 3d3,3s2(4s, 4p, 4d, 4f) ofGe XX in the LSJ coupling scheme.The present results include relativistic effects through the Breit-Pauli operator. In order to keep our calculated energy splittings as close as possible to the experimental and theoretical results complied by NIST, we attempt to correct the inaccuracies in the CI coefficients in the wavefunctions, which would lead to inaccuracies in transition probabilities, by applying a "fine-tuning" technique. Fine-tuning of the ab initio energies was donethrough adjusting, by a small amount, some diagonal elements of the Hamiltonian matrix.Comparisons are made with other available experimental and theoretical results and the accuracy of the present results is assessed.

Here we present the photoionization cross sections for the ground and metastable states of Cl-like Argon by exploiting the fully relativistic Breit-Pauli R-matrix computer codes to determine these transitions of interest. We compare our work with previous theoretical and experimental results and present a detailed investigation into the model of Ar III, the resonant structure and identification process.

The generalized oscillator strengths (GOS) of the argon transitions 3p(6)-3p(5)(3d, 4d, 5d) and 3p(6)-3p(5)4f respectively for multiple strengths l = 1,3 and l = 2,4 are determined using the wavefunctions which have been generated from the CIV3 code of Hibbert. Calculations of these generalized oscillator strengths, as a function of momentum transfer, are also carried out respectively in the configuration interaction method and in the random phase approximation with exchange. The length and velocity forms have been used in this work. The gap between the absolute values of the generalized oscillator strength obtained in the theoretical calculations and those of the experimental results of Zhu et al have been noticeably reduced in the present work for the octupole excitations to 3p(5)(3d, 4d). This is due to the configuration interaction wavefunctions. The profiles and the positions of the extrema in the generalized oscillator strength have also received particular attention in the evaluation. The results of length and velocity form studies also show that the electron correlation effects are very significant for the excitations to 3p(5)(3d, 4d) but are found to have no great influence in the positions of the extrema.

In this paper we present oscillator strengths and transition probabilities for W xlv transitions between levels arising from configurations 3d104s2,4p2,4d2, 3d104k4l (k = s,p,d,f and l = p,d,f), 3d94s24l (l = p,d,f) and 3d94s4p2. The model used to calculate these contained all configurations which can be constructed from the available orbitals (up to n = 4), with either a 3d10 or 3d9 core. The calculations were performed with the configuration interaction CIV3 program with the inclusion of relativistic effects achieved through the use of the Breit–Pauli approximation. We compare our ab initio energy levels, oscillator strengths and transition rates with other experimental and theoretical values available in the literature. There is generally good agreement when only levels with 3d10 cores are considered. The literature is sparse for levels in which the 3d-subshell is opened: for the majority of the fine-structure lines considered, there is either no comparison data available or substantial differences are found. This paper also investigates how the inclusion of relativistic effects can result in a significant redistribution of the oscillator strength from the LS calculations.

We present oscillator strengths and transition rates of E1 transitions between the fine-structure levels belonging to the configurations 3s23p5, 3s3p6, and 3s23p4nl, where nl= 4s, 5s, 6s, 4p, 5p, 3d, 4d. The calculations have used extensive configuration interaction (CI) wavefunctions, with the associated Hamiltonian matrix adjusted to ensure that the eigenenergies agree with experimental energy level data (‘fine tuning’). There are consequential small changes in the CI mixing coefficients from their ab initio values and these corrected coefficients are used in the calculation of the transition data. The method of optimization of the orbital radial functions (expressed in terms of Slater-type orbitals) is described and the radial function parameters are also presented. We show some comparisons between our work and those of earlier calculations and demonstrate how the inclusion of relativistic effects (which we achieve through the use of the Breit–Pauli approximation) can result in a substantial redistribution of the oscillator strength from the LS calculation. We also demonstrate that the fine-tuning process can make, particularly for intercombination lines, a substantial improvement in the agreement between theoretical and experimental oscillator strengths.