Ab initio effective core potentials (ECP’s) have been generated to replace the Coulomb, exchange, and core‐orthogonality effects of the chemically inert core electron in the transition metal atoms Sc to Hg. For the second and third transition series relative ECP’s have been generated which also incorporate the mass–velocity and Darwin relativistic effects into the potential. The ab initio ECP’s should facilitate valence electron calculations on molecules containing transition‐metal atoms with accuracies approaching all‐electron calculations at a fraction of the computational cost. Analytic fits to the potentials are presented for use in multicenter integral evaluation. Gaussian orbital valence basis sets are developed for the (3d,4s,4p), (4d,5s,5p), and (5d,6s,6p) orbitals of the first, second, and third transition series atoms, respectively. All‐electron and valence‐electron atomic excitation energies are also compared for the low‐lying states of Sc–Hg, and the valence‐electron calculations are found to reproduce the all‐electron excitation energies (typically within a few tenths of an eV).

Ab initio effective core potentials for molecular calculations. Potentials for the transition metal atoms Sc to Hg

Relativistic effects are defined as the difference between the case of a finite speed of light as in the world we live in and of an infinite speed of light as assumed by most theoretical chemistry. Ways in which these relativistic effects can be used to explain some of the most conspicuous anomalies in the latter half of the periodic table comprise this article. These relativistic effects are found to be particularly strong around gold in the table. (BLM)

Relativity and the periodic system of elements

Special or anomalous chemical effects are examined in relation to periodic-table trends, and the degree to which these are relativistic effects are determined. It is noted that the degree to which these relativistic effects and the introduction of 4f electrons (the usual textbook explanation of the anomalies) affect chemical behavior are of approx. equal magnitude. The anomalies that are discussed in light of relativistic effects are (1) the lanthanide contraction; (2) the inert pair effect; and (3) the unique properties of Au (as compared to Ag and Cu), of Hg (as compared to Cd and Zn), and of U/sup 6 +/, Np/sup 6 +/, and Pu/sup 6 +/ (as compared to the corresponding lanthanides). 29 references are cited. (BLM)

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Relativistic effects on chemical properties

Publisher Summary This chapter provides a summary of the relativistic calculations on multielectron or multicenter problems. The Dirac–Fock Hamiltonian and the main quantum electrodynamical (QED) corrections are discussed and the atomic and bandstructure calculations are reviewed. Then the construction of relativistic molecular orbitals and the solvable one-electron molecular and solid-state models are described. The simplest possible system for studying relativistic effects in chemical bonding is H2+. Several variational linear combinations of atomic orbitals (LCAO)-type solutions of the Dirac equation for H2+ show that the relativistic effects decrease the electronic energy by about –7 ╳ 10–6 a.u. The Dirac-Fock and Dirac-Slater molecular calculations, the relativistic semiempirical methods, and the perturbation treatments of relativistic effects are also described. In relativistic treatments of several spectroscopic properties, the entire formulation must be changed if relativistic wavefunctions are used. Some of its examples are considered. The chapter also presents a preliminary account of the relativistic effects on the chemical properties of the periodic system of elements.

Relativistic Quantum Chemistry

A multiconfigurational approach to the quantum chemistry of heavy element compounds is described. Relativistic effects are treated in two steps, both based on the Douglas–Kroll Hamiltonian. Scalar terms are included in the basis set generation and are used to determine wave functions and energies, which include static (through the use of the CASSCF method) and dynamic correlation effects (using multiconfigurational perturbation theory, CASPT2). Spin–orbit coupling is treated in a configuration interaction model, which uses CASSCF wave functions as the basis states. The method is shown to work for all atoms of the periodic system, with the possible exception of the heavier fifth row main group atoms. Illustrative results are presented for the main group atoms (spin–orbit splittings), the electronic spectrum of the iridium atom, the ground state of Tl2 and Pb2, and for the electronic spectrum of PbO. Some applications in actinide chemistry are also discussed.

P. Pyykko

Papers

Relativistic and non-relativistic Hartree-Fock one-centre expansion calculations for the series CH4 to PbH4 within the spherical approximation