摘要:

The singular value decomposition, SVD, is applied to the linear eigenvalue problem in atomic structure calculations. By comparing with recent calculations of energy levels in neutral Ca, it is shown that the SVD can give quite accurate results and much faster than normal diagonalization techniques, even of the Davidson type. However, the energy levels calculated in this approach are more strongly bound than the real eigenvalues, and this is ascribed to an artefact of the SVD, caused by the use of a discretized continuum in the calculations. This effect can lead to fairly large errors if there is strong CI present. The property of the linear eigenvalue problem that the spectrum is unchanged when a constant is added to the diagonal does not apply to the SVD. This means that it is impossible to solve the problems connected with a discretized continuum simply by shifting the spectrum.

ISSN:0026-8976    

DOI:10.1080/00268970050080483

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Results of many calculations of the MP2 correlation energies for ground states of closed-shell atoms (referred to as MP2/CA energies) are presented and studied. Special attention is paid to laying down rules which govern the dependence on the nuclear charge (Zdependence) and on the number of electrons (Ndependence) of (a) the partial wave (PW) increments to the second-order pair energies, (b) the second-order pair energies, and (c) the configurational pair energies. It has been found that these energy increments disclose many regularities useful from both the physical and computational points of view. Some of the MP2/CA increments are quasi-transferable between similar systems. The results obtained are used as a starting point for an extensive discussion of the methodological significance of MP2/CA studies, and for indicating various actual and potential areas of application of the MP2/CA approach in many-electron theory.

ISSN:0026-8976    

DOI:10.1080/00268970050080492

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) calculations have been performed for the low-lying levels 2p43P, 2p3(4S0)3s3,5S0and 2p3(4S0)3p3,5P0of neutral oxygen. Different cancellation effects on the specific mass shift, on the electronic contributions to hyperfine interaction constants and on the length and velocity forms of oscillator strengths are illustrated. The final CI values are compared with experimental values and, when available, with values from other theories.

ISSN:0026-8976    

DOI:10.1080/00268970050080500

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The part of a one-electron coefficient of fractional parentage (cfp) depending, for the atomiclshell, on the spinS, seniority υ, and electron numbernof the daughter state, is factored into two parts, the first with dependence onnand υ, and the second with dependence on υ andS. Various techniques are used to extend these results to the two-electron cfp. These entail deriving analogues of the 6-jsymbols for the symplectic group Sp(4l+ 2) and the special orthogonal group SO(2l+ 1). Explicit algebraic expressions are provided, and the choice of multiplicity indices and their circumvention are discussed.

ISSN:0026-8976    

DOI:10.1080/00268970050080519

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The possiblities of merging QED with the standard many-body perturbation theory (MBPT) for atomic systems in a rigorous and systematic way are analysed. Time-dependent MBPT, based on the time-evolution operator, a technique well developed particularly in nuclear theory, is used and somewhat reformulated to be consistent with the covariant QED formalism. An effective QED Hamiltonian, free from singularities, is constructed. The procedure can be applied to degenerate and quasi-degenerate systems (extended model space), which is not possible with the standard QED technique based upon theS-matrix formulation. To include in the model space closely lying energy levels, such as fine-structure levels, can have a dramatic effect on the convergence rate. The electron-electron interaction is investigated in detail, and it is shown that it can be separated into irreducible multi-photon interactions, which in principle can be iterated as in standard MBPT. Singularities do not appear, and a simple procedure for evaluating residual finite contributions is described. Comparison is made with the closely related Green's function technique. The procedure is presently being tested on the fine-structure levels of He-like ions.

ISSN:0026-8976    

DOI:10.1080/00268970050080528

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A basis of Hermite splines is used in conjunction with the collocation method to solve the orbital equations for diatomic molecules. Accurate solutions of the Hartree-Fock equations are obtained using iterative methods over most regions of space, while solving the equations by Gaussian elimination near the nuclear centres. In order to improve the speed and accuracy of our iterative scheme, a new self-adjoint form of the Hartree-Fock equation is derived. Using this new equation, our iterative subroutines solve the Hartree-Fock equations to one part in 106. The Gaussian elimination routines are accurate to better than one part in 108.

ISSN:0026-8976    

DOI:10.1080/00268970050080537

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The reduced multireference coupled cluster method with singles and doubles (RMR CCSD) is extended to handle high spin open-shell systems within the framework of the unitary group based coupled cluster theory (UGA CCSD). The method is applied to several states of multiply bonded diatomics, namely to the X2

ISSN:0026-8976    

DOI:10.1080/00268970050080546

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Nuclear distributions affect many aspects of atomic spectra, making atomic physics a useful tool to study also nuclear properties. Relativistic coupled-cluster calculations for the 7s and 7p states in Fr are presented and applied to binding energies, and to electronic factors for the field isotope shift. The result,F

ISSN:0026-8976    

DOI:10.1080/00268970050080555

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A number of ideas and methods for theoretical studies of the structure and spectra of many-electron systems are considered. The main emphasis is on the self-consistent field method in various approximations: single- and multi-configuration approaches, analytical and numerical radial wavefunctions, and general methods of calculation of spin-angular parts of various matrix elements. The importance is stressed of the use of the second quantization and quasispin technique in coupled tensorial form.

ISSN:0026-8976    

DOI:10.1080/00268970050080564

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268970050080573

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor