Many-Body Approach to Hyperfine Interaction in Atomic Nitrogen (original) (raw)
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Study of the 1s and 2s shell contributions to the isotropic hyperfine coupling constant in nitrogen
Journal of Physics B: Atomic, Molecular and Optical Physics, 1988
The istropic part of the hyperfine coupling constant is investigated by means of multireference configuration interaction calculations employing Gaussian basis sets. A detailed study of the 1s and 2s spin polarisation in the nitrogen atom and the NH molecule shows that the structure of the lower-energy space of the unoccupied orbitals is essential for the results. A contraction of the Gaussian basis is possible without loss of accuracy if enough flexibility is retained to describe the main features of the original space of unoccupied functions. Higher than double excitations are found to be non-negligible for the description of aiso.
Correlation Energy of Atomic Nitrogen
Physical review, 1972
The Brueckner-Goldstone many-body perturbation theory is applied to stu the electronic structure of the atomic nitrogen in its ground 4$ state. A complete orthonormal set of the V" single-particle states with angular symmetry up to) = 5 is explicitly used to calculate the correlationmnergy diagrams. The contribution from higher l (& 5) is estimated by a hydrogenic approximation of the continuum wave functions. Our final correlation energy is-0.1895 + 0.003 a.u. , as compared with-0.1886+ 0.0094 a.u. from the semiempirical estimate made by Veillard and Clementi. The sum of the exchange-core-polarization and pair-correlationenergy diagrams give a total of-Q. 207 28 a.u. , which is 110% of the semiempirical estimate. This contains a contribution of-0.00610 a.u. (3.2 %} from L &3 states and-0.05825 a.u. (31 %) from the excitations into the valence 2p orbitals, the latter arising from the open-shell nature of the nitrogen atom. The overestimate (10 %) of the correlation energy is remedied by the pair-pair correlation of 0. 01137 a. u. (6%) and the many-electron (three and four) effect of 0.00642 a.u. (3.4 %). A comparison with earlier configuration-interaction results is also made.
Many-Body Theory for Hyperfine Effects in Atoms and Molecules
Journal de physique. Colloque, 1970
RCsumC.-Comnle exemple d'application de la theorie des perturbations A N-corps, nous avons etudie le probleme de la constante J~r n de couplage spin-spin nucleaire indirect dans la molCcule HD. L'ensenible cornplet d'etats utilise est exactement celui des etats des spectres discret et continu de I'ion moleculaire H;, avec la mCme separation internucleaire que pour la molecule HZ. Notre valeur calculee de J H D par le mecanisme d'interaction de contact de Ferrni est 42,57 Hz, alors que la plus recente valeur experimentale est de 42,l : 0,l Hz.
The Journal of Chemical Physics, 1992
The hyperfine coupling constants (hfcc) Aiso and Aij are calculated for the atoms of NH2 in its two lowest-lying electronic states at various molecular geometries by means of the ab initio multireference configuration interaction method. The vibronically averaged values of the hfccs for the K=0 and 1 levels in 14N 1H2 in the energy range up to 20 000 cm−1 are computed. Polarization effects which determine Aiso as well as a simple model to describe the dipolar hfccs are discussed. All results are in excellent agreement with experimental data.
Many-body aspects of the parameterization of the hyperfine and other atomic interactions
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1987
The idea of the parametrization of atomic interactions, such as the hyperfine interaction, the spin-orbit interaction and the isotopic field shift, is reviewed from the point of view of atomic many-body theory. The close analogy between Goldstone perturbation diagrams and the angular-momentum diagrams of Jucys et al. is used extensively in the analysis. In the non-relativistic limit, when only electrostatic perturbations are considered, it is verified that the hyperfine interaction can be exactly described by the effective onebody operator, introduced by Harvey, provided LS-dependent parameters are used. When relativity is considered, it is shown that the consideration of effective one-body effects leads to the theory of Sandars and Beck, with LS-independent parameters, while the remaining effects can be represented by LS-dependent one-body operators of higher tensor ranks.
Calculation of hyperfine coupling constants
Molecular Physics, 1987
The hyperfine coupling constant for the nitrogen atom is evaluated by large-scale MRD-CI calculations. A detailed analysis of the charge density at the nucleus and the spin polarization in the ls and 2s shell as a function of various technical parameters is undertaken. Various (s, p) AO basis sets and the inftuence of correlation orbitals is investigated as weil as selection threshold and other properlies in CI calculations. The best value, obtained for the isotropic hyperfine coupling constant in an s, p, d basis, based on theoretical judgment of' best' quantities, is 9·9 MHz compared to 10·4509 MHz.
Ab Initio Calculation of Hyperfine Interaction Parameters: Recent Evolutions, Recent Examples
Hyperfine Interactions, 2004
For some years already, ab initio calculations based on Density Functional Theory (DFT) belong to the toolbox of the field of hyperfine interaction studies. In this paper, the standard ab initio approach is schematically sketched. New features, methods and possibilities that broke through during the past few years are listed, and their relation to the standard approach is explained. All this is illustrated by some highlights of recent ab initio work done by the Nuclear Condensed Matter Group at the K.U.Leuven.
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1989
Multi-reference configuration interaction calculations employing various orbital transformations are undertaken to obtain the isotropic hyperfine coupling constant aiso in nitrogen and ais 0 (H) in the CH molecule. The natural orbital (NO) basis is found to be more effective than the simple RHF-MO basis; the most obvious is a basis of spin natural orbitals (SNO). lt is found that a 180 is approached from opposite sides in the NO and 2s shell SNO basis if the CI expansion is increased. Both results are within a few percent of the full CI Iimit for the nitrogen atorn (in the given AO basis) and the experimental value for Hin the CH radical. Various features ofthe SNO are discussed.
Physical Review A, 1997
To enhance the current understanding of mechanisms contributing to magnetic hyperfine interactions in excited states of atomic systems, in particular, alkali-metal atom systems, the hyperfine fields in the excited 5 2 S 1/2-8 2 S 1/2 states of potassium and 8 2 S 1/2-12 2 S 1/2 states of francium atoms have been studied using the relativistic linked-cluster many-body perturbation procedure. The net theoretical values of the hyperfine fields for the excited states studied are in excellent agreement with available experimental data for both atoms. There is a significant decrease in importance of the correlation contribution in going from the ground state to the excited states, the correlation contributions as ratios of the direct contribution decreasing rapidly as one moves to the higher excited states. However, the contribution from the exchange core polarization ͑ECP͒ effect is nearly a constant fraction of the direct effect for all the excited states considered. Physical explanations are offered for the observed trends in the contributions from the different mechanisms. A comparison is made of the different contributing effects to the hyperfine fields in potassium and francium to those in the related system, rubidium, studied earlier. Extrapolating from our results to the highly excited states of alkali-metal atoms, referred to as the Rydberg states, it is concluded that in addition to the direct contribution from the excited valence electron to the hyperfine fields, a significant contribution is expected from the ECP effect arising from the influence of exchange interactions between electrons in the valence and core states. ͓S1050-2947͑97͒07907-9͔
Long-range interactions of hydrogen atoms in excited states. III. nS−1S interactions for n≥3
Physical review, 2017
The long-range interaction of excited neutral atoms has a number of interesting and surprising properties, such as the prevalence of long-range, oscillatory tails, and the emergence of numerically large van der Waals C6 coefficients. Furthermore, the energetically quasi-degenerate nP states require special attention and lead to mathematical subtleties. Here, we analyze the interaction of excited hydrogen atoms in nS states (3 ≤ n ≤ 12) with ground-state hydrogen atoms, and find that the C6 coefficients roughly grow with the fourth power of the principal quantum number, and can reach values in excess of 240 000 (in atomic units) for states with n = 12. The nonretarded van der Waals result is relevant to the distance range R ≪ a0/α, where a0 is the Bohr radius and α is the fine-structure constant. The Casimir-Polder range encompasses the interatomic distance range a0/α ≪ R ≪ c/L, where L is the Lamb shift energy. In this range, the contribution of quasi-degenerate excited nP states remains nonretarded and competes with the 1/R 2 and 1/R 4 tails of the pole terms which are generated by lower-lying mP states with 2 ≤ m ≤ n − 1, due to virtual resonant emission. The dominant pole terms are also analyzed in the Lamb shift range R ≫ c/L. The familiar 1/R 7 asymptotics from the usual Casimir-Polder theory is found to be completely irrelevant for the analysis of excited-state interactions. The calculations are carried out to high precision using computer algebra in order to handle a large number of terms in intermediate steps of the calculation, for highly excited states.