Partial photoionization cross sections and angular distribution asymmetry parameters for atomic xenon have been calculated in the relativistic random-phase approximation for 26 jj-coupled channels over a wide range of energies (0 -1 keV). The effects of relaxation on the 4d and 3d cross sections are examined by using a modification of the relativistic random-phase approximation that calculates excited-state orbitals in the potential of the relaxed ion. Results are compared with Hartree-Fock theory, with the nonrelativistic random-phase approximation, and with recent photoemission experiments.

The transient, collision-induced changes in electric properties of ion–atom or atom–atom pairs at long range are determined by the polarizabilities and hyperpolarizabilities of each of the interacting species. Induction effects on moments of the charge distribution or static susceptibilities depend on the response at zero frequency, and dispersion effects depend on the polarizabilities (linear and nonlinear) at imaginary frequencies. In this paper, we give numerical results for four static multipole hyperpolarizabilities of the helium atom obtained from large-basis, ab initio calculations using many-body perturbation theory and coupled-cluster methods. We report and analyze the numerical results for the R−6 and R−8 terms in the dispersion contributions to the He–He, He–H, and H–H pair polarizability functions with a corrected formula for the contributions from the P-hyperpolarizability tensor. For both parallel and perpendicular components of the polarizability, the numerical results at order R−8 have contributions of similar magnitude arising from the terms containing the P and Q hyperpolarizabilities; these terms approximately cancel for Δα⊥, but reinforce for Δα∥. When R is near to or smaller than the van der Waals minimum distance, the dispersion series is damped by overlap, but the ratio of the undamped R−6 and R−8 terms gives a guide to the convergence behavior. For the pairs treated here, the R−6 and R−8 terms in Δα∥ become equally important between 5 and 8 bohr, but the R−6 term dominates the series for Δα⊥ down to separations of 3–4.5 bohr.

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The electronic structures of the fullerenes, characterized by π-electron systems spread over a closed surface, may exhibit novel responses to external electric and magnetic fields. Accurate theoretical determination of such properties is made difficult by the large number of electrons, but for some systems, in particular C 60, the molecular symmetry can be taken into account to achieve significant reduction in computer effort. A method has been developed that permits the use of the full molecular point group symmetry in the calculation of perturbed electron. density matrices transforming as second-rank tensors. In this note preliminary coupled Hartree-Fock results in a minimal basis for static electric response properties of C 60 (the second electric dipole hyperpolarizability γ, the electric quadrupole polarizability C and the first electric (mixed) dipole-quadrupole hyperpolarizability B) are presented.