Berylliumlike Systems Research Articles

Semiclassical calculations of the quadruple excited four-electron systems

Highly excited atoms acquire very large dimensions and can be present only in a very rarified gas medium, such as the interstellar space. Multiply excited beryllium-like systems, when excited to large principal quantum numbers, have a radius of r ? 10 ?. We examine the semiclassical spectrum of quadruple highly excited four-electron atomic systems for the plane model of equivalent electrons. The energy of the system consists of rotational and vibrational modes within the almost circular orbit approximation, as used in a previous calculation for the triply excited three-electron systems. Here we present numerical results for the beryllium atom. The lifetimes of the semiclassical states are estimated via the corresponding Lyapunov exponents. The vibrational modes relative contribution to the energy levels rises with the degree of the Coulombic excitation. The relevance of the results is discussed both from the observational and heuristic point of view.

Relativistic MCSCF by means of quasidegenerate direct perturbation theory. II. Preliminary applications

The relativistic multiconfiguration self-consistent field (MCSCF) theory by means of (quasidegenerate) direct perturbation theory (DPT) is formulated and implemented through the leading order. Systematic investigations of nondynamical correlation and relativistic effects in berylliumlike systems are carried out. For this sequence, it appears that the single-state first-order DPT is valid only for the nuclear charge up to 30 or so. Calculations for the spectroscopic constants of the molecules of homonuclear halogen dimers X2 (X=F, Cl, Br, I, At) and TlX (X=F, Cl, Br, I) are performed at all-electron SCF (self-consistent field) and complete active space SCF levels, with the aim to demonstrate the efficiency of DPT by comparing with other relativistic calculations. Spin–orbit coupling affects the energies of the open-shell atoms and is taken into account for the binding energies.

Ionization potential for ground states of berylliumlike systems.

The 1s 2 2s 2 ground-state energies of berylliumlike systems are calculated with a full-core plus correlation method. A partial saturation of a basis-function method is used to extrapolate a better nonrelativistic energy. The 1s 2 2s 2 ionization potentials are calculated by including the relativistic corrections, mass polarization, and QED effects. These results are compared with the existing theoretical and experimental data in the literature. The predicted Be I, C III, N IV, and 0 V ionization potentials are within the quoted experimental error

Identification of high resolution Auger spectra of boron and beryllium

Sixteen B II and thirteen Be I 1s2l2l'2l" states are calculated with multi-configuration interaction wavefunctions. Relativistic and mass polarisation corrections are included. The energies obtained are used to calculate the energies of the Auger electrons in the (1s22s,e) and (1s22p,e) decay processes. These results are used to identify the recalibrated high resolution spectra of Rodbro, Bruch and Bisgaard (1979). Many new identifications are made. It is found that with the electron energy in the range 150-180 eV, all lines observed in the B II spectrum with significant intensity are either coming from 1s2l2l' lithium-like systems or 1s2l2l'2l" beryllium-like systems. For beryllium, the author's results are used to identify the previously unidentified lines in the observed spectrum. For both B II and B I, the agreement between the result and the experiment is excellent.

The Dirac equation in the algebraic approximation

The construction of variational approximations to the solutions of the Dirac equation is discussed. The importance of imposing the physical boundary conditions for both the point- and finite-nuclear models on the set of trial functions is emphasised. The low-frequency Breit interaction is shown to cause no variational failure when included in the iterative solutions of the Dirac-Hartree-Fock equations. The practical advantages of calculations which variationally include the Breit interaction over conventional treatments which employ only the Coulomb interaction are discussed. Manybody perturbation theory calculations of the radial correlation energy of helium- and beryllium-like systems are reported