P. Schwerdtfeger (Editor) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Relativistic Electronic Structure Theory, Part 2: Applications Theoretical and Computational zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Chemistry, Vol. 14 9 2004 Elsevier B.V. All rights reserved. 81 Chapter 2 Accurate Relativistic Fock-Space Calculations for Many-Electron Atoms Uzi Kaldor, Ephraim Eliav, and Arie Landau School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel Abstract High-accuracy results for energy levels of heavy and superheavy atoms are presented. The projected (or no-virtual-pair) Dirac-Coulomb-Breit Hamiltonian serves as the starting point and defines the physical frame- work. One-electron four-component Dirac-Fock-Breit functions, similar in spirit to Hartree-Fock orbitals in the nonrelativistic formulation, are cal- culated first, followed by treatment of electron correlation. Correlation is included by the Fock-space coupled cluster method. The recent intermedi- ate Hamiltonian approach makes it possible to use larger and more flexible P (model) spaces, thereby extending the range of applicability to states not accessible before. Accuracy is greatly improved for systems which can be treated by both methods, and the model space structure can be stud- ied and pushed to convergence for the first time. Applications address mostly transition energies (ionization potentials, excitation energies, elec- tron affinities) in various atoms. Very large basis sets, going up to I = 8, are used. High-/orbitals are particularly important for transitions involving f electrons. The outer 20-40 electrons of the atom are correlated. The Breit term is required for fine-structure splittings and for f transitions. Repre- sentative applications are described, including electron affinities of alkali atoms, obtained within 5 meV of known experimental values and providing the best estimate of the experimentally unknown EA of francium; the gold atom, with relativistic effects of 3-4 eV on transition energies; and Pr 3+, where the many f2 levels are reproduced with great precision. The most exciting aspect of the high accuracy provided by the method is the ability to obtain reliable predictions for superheavy elements, where level ordering (and therefore chemistry) may differ from that of the lighter homologues. Thus, the ground state of eka-gold (El11) is 6d97s 2, rather than the 6dl~