[en] Published in summary form only

[en] Published in summary form only

No abstract available

[en] The 2p⁵3s ¹P₁, ³P₁-2p⁵3p ¹S₀ transitions in Ne-like Ti XIII have been identified by beam-foil spectroscopy. The term value derived for the 3p¹S₀ level is used for improved predictions along the isoelectronic sequence by means of comparison with theoretical calculations. Accurate predictions of the magnetic dipole (M1) transition 2p⁵3s ³P₀-³P₁ along the sequence are also made. (orig.)

[en] The exact, four-component second-order Dirac equation in transformed elliptical coordinates is derived for a diatomic system. Numerical solutions are obtained using a point-relaxation approach. The relativistic correction to the total energy of H₂⁺ at R = 2 a.u. is found to be -7.365x10^-6 a.u. The deviation from an earlier value of -7.383x10^-6 a.u. by Luke et al. or by Bishop is shown to arise from a spuriously large c^-4 term in their Hamiltonian. (orig.)

[en] In the introduction we remind the reader of the conceptual differences between the unboundedness of the Dirac hamiltonian, the Brown-Ravenhall and the basis set diseases, and of the methods to cure the latter. Then the theoretical interpretation of relativistic changes of bond lengths Δ_relR is worked out using only very elementary mathematics. The theoretical expression for Δ_relR can be split up into two contributions which are not individually invariant against unitary transformations. The first contribution is given by the expectation value of the relativistic correction of the Hellmann-Feynman force, <δ²V/δRδln c²>. It may be neglected in standard two- or four-component all-electron calculations. On the other hand it seems to be the dominant contribution in pseudopotential valence-only calculations, but has sometimes been overlooked in the literature. The second contribution is the dominant one in all-electron calculations. It can be expressed in two alternative forms, which give rise to two complementary interpretations (IIa) and (IIb). They both differ from the one (I) appropriate for pseudopotential calculations. Whilst interpretation IIa is generally accepted in the literature, interpretation IIb although equivalent is often refused. The two interpretations differ in emphasizing the potential or kinetic energies, the bond or inner shell regions, the density changes due to relativity or due to overlapping, respectively. (orig.)

[en] It is shown that matrix representations of the Dirac equation give stable positive energy eigenstates if the large and small component bases are kinetically balanced. Results are presented for relativistically optimized basis sets using a Gaussian charge model for the nucleus. Some recent results for many-electron systems are compared with previously obtained results of other authors. (orig.)

[en] The ratio of the atomic electric dipole moment (EDM) to a possible electron EDM has been calculated for the ground states of Cs, Xe and Hg, including to all orders the diagrams that involve only single excitations, while neglecting correlation effects, which require the simultaneous excitation of two or more electrons. The alkali atoms are known to have large enhancement factors and as a test of the procedure, a calculation was performed for the Cs ground state. The lowest experimental limit for an atomic EDM, so far has been established for the ground state of Xe, which is a closed-shell system, where the simple mechanisms for producing an atomic EDM from an electronic one are not available, but the interaction with the nuclear magnetic moment may still give an atomic EDM, which is here found to be about 10^-3 of the electron EDM. For the heavier atom Hg, the effect is an order of magnitude larger. (orig.)

[en] Nonrelativistic, relativistic and semiempirical pseudopotentials have been used for investigating the effects of relativity and correlation on molecular properties (bond lengths, dissociation energies, force constants, multipole moments and ionization energies) of TlH⁺, TlH and TlH₃. Spin-orbit effects are taken into account by using a quasirelativistic two-component pseudo-potential. The influence of the core-valence correlation is accounted for by a core-polarization potential. Results obtained with the semiempirical pseudopotentials are in good agreement with experiment. (orig.)

[en] This article discusses our measurement of the Lamb shift in heliumlike uranium and outlines future tests of QED using few-electron very high atomic number (Z) ions. Our recently reported Lamb shift value of 70.4 (8.3)eV for the one-electron Lamb shift in uranium is in agreement with the theoretical value of 75.3 (0.4)eV. The experimental value was extracted from a beam-foil time-of-flight measurement of the 54.4 (3.4)ps lifetime of the 1s2p_1/2³P₀ state of helium-like uranium. (orig.)