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The Rayleigh-Schrodinger perturbation formalism is extended to the case of a model space, which is not necessarily degenerate. The model space defines the zero-order or model wavefunction, and the new formalism makes it possible to use a model wavefunction of multi-configurational type. The effect of the states outside the model space are as usual taken into account by means of a perturbation expansion and expressed in terms of an 'effective' Hamiltonian, operating only within the model space. The extended Rayleigh-Schrodinger formalism is used to prove the linked-diagram theorem for a multi-configurational model space in a simple way. Alternatively, this pfoblem can be handled by means of the well known formalism for degenerate perturbation, treating the splitting within the model space as due to an additional perturbation. The present approach, however, is more direct and the model space splitting is handled without summing any infinite series. The problem of convergence of the perturbation expansion is briefly discussed.

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A new approach to the diagrammatic formulation of many-body perturbation theory for open-shell systems is presented. The formalism is based on a generalized form of the Bloch equation that also generates the Rayleigh-Schrodinger perturbation expansion for a system with several open shells. Second quantization in the particle-hole formulation is used together with Wick's theorem in order to derive graphical rules in the usual way. The linked-diagram property of the wave operator and of the effective interaction is shown by expanding the wave operator in terms of normal products of connected diagram clusters, in analogy with the exp(S) formalism of Coester and Kiimmel for closed-shell systems. Self-consistent "coupled-cluster'' equations are derived for the open-shell case from the generalized Bloch equation by a straightforward extension of the procedure of &ek and Paldus. The application of such equations for investigating different properties of open-shell atoms is discussed.

We present a detailed theoretical evaluation for the g j factor of a bound electron in hydrogenlike ions up to Zϭ94. All quantum electrodynamical corrections of order (␣/) are evaluated in detail and various other contributions to the g j factor are computed and listed for 61 Z. A comparison with all existing experiments is carried out and excellent agreement is found. The present uncertainty in our calculations is discussed. It is not possible to improve this precision with only minor effort since two-photon bound-state QED terms are uncalculated up to now.

Library of Congress Cataloging-in-Publication Data. Lindgren, Ingvar, 1931-. Atomic many-body theory. (Springer series in atoms + plasmas; 3) "The first edition was published in 1982 in Springer series in chemical physics, vol. I3"--T.p. verso. Bibliography: p. Includes indexes. I. Atomic theory. 2. Many-body problem. I.

In view of the current interest of QED in strong fields, a complete set of one-photon radiative corrections to the bound-electron g factor is evaluated for several hydrogenlike ions. The calculations are performed to all orders in the nuclear potential and compared to earlier results, based on the (Z␣) expansion, which includes the Schwinger and the Grotch terms. For low Z our all-order result approaches the (Z␣) expansion, but for high Z there is a substantial deviation. Furthermore, for high Z our calculations show that the uncertainty due to nuclear structure is small and thus strongly motivate the bound g-factor experiment in progress. ͓S1050-2947͑97͒50410-0͔