Breit-Pauli Approach Research Articles

Expectation Values of the Neutral Chromium Radius

Neutral Chromium (Cr I) is an important element in many laboratory plasma applications. In this work, expectation values of the radius for Cr I are calculated. These atomic data are calculated with three different atomic codes: Cowan code using the Hartree–Fock Relativistic approximation, SUPERSTRUCTURE and AUTOSTRUCTURE codes using scaled Thomas–Fermi–Dirac–Amaldi potential. Relativistic corrections are introduced according to the Breit–Pauli approach. The 3 d 5 4 s , 3 d 4 4 s 2 , 3 d 5 4 d , 3 d 5 4 p and 3 d 4 4 s 4 p configurations are included to obtain the expectation values of radius of Cr I and compared with available data. The novelty of our work is to obtain new values of < 1 r > , < r > , and < r 2 > for the configuration of 4 p and 4 d and the values of < r 3 > for all orbitals configurations considered in this work.

Fine structure collision strengths for S VII lines

Energy levels, oscillator strengths, radiative decay rates and fine structure collision strengths are presented for six times ionized sulfur S VII. The atomic data are calculated with the SUPERSTRUCTURE code, where relativistic corrections are introduced according to the Breit–Pauli approach. We include in this work the (1s2) 2s22p6, 2s22p53l, 2s2p63l, 2s22p54l (l ⩽ n − 1) configurations that yield the lowest 75 levels. The scattering problem is treated in the distorted wave approach by the code DISTORTED WAVE. This produces collision strengths in LS coupling that will be used by the code JAJOM to transform them into fine structure ones. Fine structure collision strengths for transitions from the ground and the first four excited levels are presented at six electron energies from 20 to 120 Ryd by a step of 20 Ryd. Our atomic structure data are compared with the available experimental and theoretical results.

Quantifying the strength and asymmetry of giant resonances in the photorecombination ofSc3+and the photoionization ofSc2+

We report on strong interference effects for the dominant, highly correlated, broad, and asymmetric 3p53d2(2F5/2,7/2o) giant resonances in the photorecombination of Sc3+. Using a nonorthogonal perturbative multiconfiguration Breit-Pauli approach, we present theoretical photorecombination cross sections that are in line with the Test Storage Ring measurements of Schippers et al. In order to reproduce the observed asymmetric resonance profiles near threshold, it was necessary to include resonance-continuum interference. Also, we present Sc2+ photoionization cross sections that agree with the Advance Light Source measurements of Schippers et al. This perturbative method is based on analytical expressions for the cross sections in terms of computed energies and transition rates, thereby directly determining resonance strengths and Fano asymmetry parameters. Of particular note, our reported absolute cross sections are in excellent agreement with experimental results, in contrast to all previous theoretical calculations. Furthermore, the apparent violation of the sum rule prediction, determined both from our integrated photoionization cross sections and from experimental results, is found to be due to radiative damping of narrow resonances.

The role of atomic correlations in the theoretical study of minor actinide ions

This paper aims to demonstrate the recent possibilities to account for correlation and relativistic effects in studying the electronic structure and energy spectra of actinide ions. The fine structure of lowest term 7 F of tetravalent curium (Cm 4+) is considered as an example, as part of an ongoing project to understand the unexpected ground-state properties of this peculiar ion. The calculations were performed in multiconfiguration Hartree–Fock (including relativistic effects in the Breit–Pauli approach) and multiconfuguration Dirac–Fock approximations. The results obtained demonstrate that, whilst core–valence and core–core correlations are essential to assess correctly the Cm 4+ term energy, their role in the determination of the fine structure is much less important compared to that of valence–valence correlations.

Inclusion of Electric Octupole Contributions Explains the Fast Radiative Decays of Two Metastable States inAr+

A laser probing investigation has yielded the lifetimes of the 3s(2)3p(4)(1D)3d (2)G(7/2,9/2) metastable doublet states of Ar+. The results, obtained with the CRYRING ion storage ring of Stockholm, are 3.0+/-0.4 and 2.1+/-0.1 s, respectively. Comparisons with theoretical values calculated with two independent theoretical approaches, i.e., the pseudorelativistic Hartree-Fock method and the multiconfiguration Breit-Pauli approach, have allowed us to establish the unexpected and extraordinary strong contribution of an electric octupole (E3) transition to the ground state, in addition to the M1 decay channels to the 3d ;{2,4}F states and the E2 contributions to the 4s 2P, 2D states.

Relativistic heavy-atom effects on heavy-atom nuclear shieldings

The principal relativistic heavy-atom effects on the nuclear magnetic resonance (NMR) shielding tensor of the heavy atom itself (HAHA effects) are calculated using ab initio methods at the level of the Breit-Pauli Hamiltonian. This is the first systematic study of the main HAHA effects on nuclear shielding and chemical shift by perturbational relativistic approach. The dependence of the HAHA effects on the chemical environment of the heavy atom is investigated for the closed-shell X(2+), X(4+), XH(2), and XH(3) (-) (X=Si-Pb) as well as X(3+), XH(3), and XF(3) (X=P-Bi) systems. Fully relativistic Dirac-Hartree-Fock calculations are carried out for comparison. It is necessary in the Breit-Pauli approach to include the second-order magnetic-field-dependent spin-orbit (SO) shielding contribution as it is the larger SO term in XH(3) (-), XH(3), and XF(3), and is equally large in XH(2) as the conventional, third-order field-independent spin-orbit contribution. Considering the chemical shift, the third-order SO mechanism contributes two-thirds of the difference of approximately 1500 ppm between BiH(3) and BiF(3). The second-order SO mechanism and the numerically largest relativistic effect, which arises from the cross-term contribution of the Fermi contact hyperfine interaction and the relativistically modified spin-Zeeman interaction (FC/SZ-KE), are isotropic and practically independent of electron correlation effects as well as the chemical environment of the heavy atom. The third-order SO terms depend on these factors and contribute both to heavy-atom shielding anisotropy and NMR chemical shifts. While a qualitative picture of heavy-atom chemical shifts is already obtained at the nonrelativistic level of theory, reliable shifts may be expected after including the third-order SO contributions only, especially when calculations are carried out at correlated level. The FC/SZ-KE contribution to shielding is almost completely produced in the s orbitals of the heavy atom, with values diminishing with the principal quantum number. The relative contributions converge to universal fractions for the core and subvalence ns shells. The valence shell contribution is negligible, which explains the HAHA characteristics of the FC/SZ-KE term. Although the nonrelativistic theory gives correct chemical shift trends in present systems, the third-order SO-I terms are necessary for more reliable predictions. All of the presently considered relativistic corrections provide significant HAHA contributions to absolute shielding in heavy atoms.

Quasirelativistic Hartree-Fock equations consistent with Breit-Pauli approach

The properties of the quasirelativistic Hartree-Fock equations are investigated. Different ways of forming the equations are discussed. The relativistic corrections employed in the traditional quasirelativistic Hartree-Fock equations are compared with the ones used within the Breit-Pauli approach. The two-electron contact interactions are revised and the new versions of the quasirelativistic Hartree-Fock equations are considered. The solutions of these equations are compared among themselves and also with those obtained within the Dirac-Fock and nonrelativistic Hartree-Fock approaches. Solution data are provided for some heliumlike, neonlike, and mercurylike ions.

Radiative and Collisional Atomic Data for Neon-like Silicon

Energy levels, line strengths, weighted oscillator strengths, radiative decay rates and electron-impact collision strengths are presented for neon-like Si V which is important for astrophysical and laboratory plasmas.Atomic data are calculated with the SUPERSTRUCTURE package using scaled Thomas-Fermi-Dirac-Amaldi potentials. Relativistic corrections are introduced according to the Breit-Pauli approach. The 1s22s22p6, 1s22s22p53l, 1s22s2p63l and 1s22s22p54l (l ≤ n - 1) configurations are included to obtain the corresponding 75 energy levels of Si V. Non-relativistic collisional data are calculated using the UCL-Distorted Wave code which are transformed to fine-structure data by UCL-JAJOM code. The collision strengths are obtained for seven incident impact electron energies: 15, 30, 45, 60, 75, 90 and 105 Ry. Some of these data are compared with available experimental andtheoretical data.

Application of Gaussian-2 theory for the energetics of XO/XO+/XO- and XOH/XOH+ (X = F, Cl, Br, I)

The Gaussian-2 (G2) procedure, with spin-orbit coupling correction estimated by the Breit-Pauli approach, is applied to study the energetics of XO/XO+/XO- and XOH/XOH+(X = F Cl Br, I). Accurate thermochemical data for these environmentally important species, in particular for the anions and iodine containing species, have not been accurately determined experimentally. For example, for IO the reported experimental heat of formation varies from -109 kJ mol-1 to 177 kJ mol-1 Using the G2 results it is now possible to recommend a set of self-consistent thermochemical data of heats of formation, ionization energies, electron affinities, proton affinities and bond dissociation energies for XO and related species. In general, among the disparate experimental data, the more recently reported heats of formation for FO-, BrO+, BrO-, BrOH, BrOH+, IO, IO+, IO-, IOH, IOH+ are found to be in good agreement with the G2 results.

Application of Gaussian-2 theory for the energetics of XO/XO+ /XO- and XOH/XOH+ (X = F, Cl, Br, I)

The Gaussian-2 (G2) procedure, with spin-orbit coupling correction estimated by the Breit-Pauli approach, is applied to study the energetics of XO/XO+/XO- and XOH/XOH+(X = F Cl Br, I). Accurate thermochemical data for these environmentally important species, in particular for the anions and iodine containing species, have not been accurately determined experimentally. For example, for IO the reported experimental heat of formation varies from -109 kJ mol-1 to 177 kJ mol-1 Using the G2 results it is now possible to recommend a set of self-consistent thermochemical data of heats of formation, ionization energies, electron affinities, proton affinities and bond dissociation energies for XO and related species. In general, among the disparate experimental data, the more recently reported heats of formation for FO-, BrO+, BrO-, BrOH, BrOH+, IO, IO+, IO-, IOH, IOH+ are found to be in good agreement with the G2 results.

Effect of configuration interaction and relativity on oscillator strengths for sodium-like systems

Oscillator strengths of both length and velocity forms, for the inner-shell excitation 1s 22s 22p 63s 2 SskJ/e→1s 22s 22p 53s 22 PskJ/0 transition in the sodium isoelectronic sequence have been calculated employing the Tiwary approach for the configuration interaction effect and the Breit-Pauli approach for the relativistic effect. Our results demonstrate that the configuration interaction effect is more important than the relativistic effect for the lowly ionized atoms and the reverse is true for the highly ionized atoms.

Theoretical study of the transition probabilities among the three lowest electronic states of the SeS molecule

Spin-perturbed CI wavefunctions are reported for the X 3Σ− electronic states of the SeS molecule. The Breit-Pauli approach is employed using the one- and two-electron spin-orbit operator as the perturbing hamiltonian and a zeroeth-order basis of CI eigenfunctions generated by the standard multireference single- and double-excitation (MRD-CI) formalism. Transition moments are reported between each of the above states for electric and magnetic dipole and electric quadrupole radiative processes, and these results are compared with recent experimental high resolution data obtained by Fink, Kruse, Ramsay and Wang. Generally good agreement is found between computed and observed ratios of such quantities, but the absolute values of the computed transition moments are uniformly found to be only somewhat less than half as large as the corresponding observed results. A simple formula is presented which relates the magnetic moments of the b 1Σ+-X 3Σ1− transitions to twice the square root of the ratio of two observab...