| 51. |
- Verdebout, Simon, et al.
(författare)
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Atomic properties of neutral Ne using the LCFI method
- 2011
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Ingår i: Abstracts 43rd Conference of the European Group for Atomic Systems (EGAS). - : European Physical Society. ; , s. 156-156
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The localised correlation function interaction (LCFI) method, based on the biorthonormal orbital transformations and e cient counter-transformations of the con guration interaction eigenvectors [1], was shown to be e cient for describing the total energy of the beryllium atom [2]. Each localized correlation function (LCF) is dedicated to the description of the electronic correlation associated to a given electron pair. Such functions are produced, using the multicon guration Hartree-Fock (MCHF) and Dirac-Hartree-Fock (MCDHF) variational methods, by optimizing the correlation functions and the mixing coe cients on a tailored con guration space. Applying the LCFI method to neon allows us to quantify the contribution of each localized correlation function to di erent atomic properties [3]. This investigation should turn out to be helpful in the development of e cient correlation models for larger systems. Neutral neon is a well-known benchmark example for testing many-body approaches. In the present work, we apply the LCFI method to the study of the three lowest terms 2p6 1S, 2p53s 3Po and 2p53s 1Po of neutral neon. We investigate the convergence pattern of the total energy, speci c mass shift and hyper ne structure parameters for the three considered states. These properties are computed for monitoring the quality of the total polyelectronic wave functions. We present the contribution of each LCF function on the di erent properties, and additionally discuss the multi-reference models adopted for reaching simultaneously good total and transition energies. A comparison between the results obtained with ATSP2K [4] and GRASP2K [5] should shed some light on the importance of the relativistic e ects on each LCF function.
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| 52. |
- Verdebout, Simon, et al.
(författare)
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Exploring Biorthonormal Transformations of Pair-Correlation Functions in Atomic Structure Variational Calculations
- 2010
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Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 43:7
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Tidskriftsartikel (refereegranskat)abstract
- Multiconfiguration expansions frequently target valence correlation and correlation between valence electrons and the outermost core electrons. Correlation within the core is often neglected. A large orbital basis is needed to saturate both the valence and core–valence correlation effects. This in turn leads to huge numbers of configuration state functions (CSFs), many of which are unimportant. To avoid the problems inherent to the use of a single common orthonormal orbital basis for all correlation effects in the multiconfiguration Hartree–Fock (MCHF) method, we propose to optimize independent MCHF pair-correlation functions (PCFs), bringing their own orthonormal one-electron basis. Each PCF is generated by allowing single- and double-excitations from a multireference (MR) function. This computational scheme has the advantage of using targeted and optimally localized orbital sets for each PCF. These pair-correlation functions are coupled together and with each component of the MR space through a low dimension generalized eigenvalue problem. Nonorthogonal orbital sets being involved, the interaction and overlap matrices are built using biorthonormal transformation of the coupled basis sets followed by a counter-transformation of the PCF expansions. Applied to the ground state of beryllium, the new method gives total energies that are lower than the ones from traditional complete active space (CAS)-MCHF calculations using large orbital active sets. It is fair to say that we now have the possibility to account for, in a balanced way, correlation deep down in the atomic core in variational calculations.
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| 53. |
- Verdebout, Simon, et al.
(författare)
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Hyperfine structures and Landé gJ-factors for n = 2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations
- 2014
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Ingår i: Atomic Data and Nuclear Data Tables. - : Elsevier. - 0092-640X .- 1090-2090. ; 100:5, s. 1111-1155
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Tidskriftsartikel (refereegranskat)abstract
- Energy levels, hyperfine interaction constants, and Landé gJ -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 doubleexcitations 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.
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| 54. |
- Verdebout, Simon, et al.
(författare)
-
Interaction of Variational Localized Correlation Functions for Atomic Properties
- 2011
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Ingår i: Abstracts 43rd Conference of the European Group for Atomic Systems (EGAS). - : European Physical Society. ; , s. 155-155
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Variational methods are used for targeting speci c correlation e ects by tailoring the con- guration space. Independent sets of correlation orbitals, embedded in the localized correlation functions (LCFs), are produced from the multicon guration Hartree-Fock (MCHF) or Dirac- Hartree-Fock (MCDHF) calculations [1,2]. These non-orthogonal functions are then coupled to each other by solving the associated generalized eigenproblem. The Hamiltonian and overlap matrix elements are evaluated using the biorthonormal orbital transformations and e cient counter-transformations of the con guration interaction eigenvectors [3]. This method was successfully applied for describing the total energy of the ground state of beryllium [4]. Moreover it has been shown that the energy convergence is faster than with the usual SD-MCHF method for which a single set of orthonormal one-electron orbitals spanning the complete con guration space is optimized. In the present work, we investigate the interaction of localized correlation functions (LCFI), not only for the 1s22s2 1S state of beryllium but also for the rst two excited states: 1s22s2p 3Po and 1s22s2p 1Po. For these three states, we evaluate the total energy but also the expectation values of the speci c mass shift (SMS) operator, the hyper ne structure (HFS) parameters and the transition probabilities. The comparison between the SMS and HFS results obtained using the LCFI method and the traditional MCHF one stresses the importance of the mixing coe cients contraction within each LCF function. We demonstrate that this unwanted contraction e ect can be bypassed by enlarging the associated generalized eigenproblem. The beryllium atom is a system for which it is still possible to saturate a single orthonormal orbital set through the complete active space MCHF expansions. As such, it constitutes the perfect benchmark for the LCFI method. For larger systems, it becomes hopeless to saturate a single common set of orthonormal orbitals, the LCFI method should be a good alternative for reaching a full-correlated wave function. The present study is a rst step in the current development of the extension of both ATSP2K and GRASP2K packages [1,2] that will adopt the biorthonormal treatment for energies, isotope shifts, hyper ne structures and transition probabilities.
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| 55. |
- Verdebout, Simon, et al.
(författare)
-
Interaction of Variational Localized Correlation Functions for Atomic Properties of Be I
- 2011
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present some progress associated to the localised correlation function interaction (LCFI) method. In this report, the LCFI method is tested not only for total energy but also for the speci c mass shift operator, the hyper ne structure parameters and the transition probabilities. These properties are computed for the three lowest electronic states of the beryllium atom. These calculations illustrate the importance of the contraction e ects.
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| 56. |
- Verdebout, Simon, et al.
(författare)
-
The Partitioned Correlation Function Interaction approach applied to B I, C II and more complex systems
- 2013
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Ingår i: Book of abstracts. - : Institute of Modern Physics, Chinese Academy of Sciences.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Synopsis The Partitioned Correlation Function Interaction (PCFI) approach has been proposed recently as a promising method for capturing e ciently electron correlation in many-electron atoms. In the present work, we apply this method to study ve-electron systems (B I and C II) and more complex atoms.
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| 57. |
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| 58. |
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| 59. |
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