Gaussian basis sets of quadruple zeta valence quality for Rb-Rn are presented, as well as bases of split valence and triple zeta valence quality for H-Rn. The latter were obtained by (partly) modifying bases developed previously. A large set of more than 300 molecules representing (nearly) all elements-except lanthanides-in their common oxidation states was used to assess the quality of the bases all across the periodic table. Quantities investigated were atomization energies, dipole moments and structure parameters for Hartree-Fock, density functional theory and correlated methods, for which we had chosen Møller-Plesset perturbation theory as an example. Finally recommendations are given which type of basis set is used best for a certain level of theory and a desired quality of results.

Various contracted Gaussian basis sets for atoms up to Kr are presented which have been determined by optimizing atomic self-consistent field ground state energies with respect to all basis set parameters, i.e., orbital exponents and contraction coefficients.

Contracted Gaussian basis sets of triple zeta valence (TZV) quality are presented for Li to Kr. The TZV bases are characterized by typically including a single contraction to describe inner shells and three basis functions for valence shells. All parameters-orbital exponents and contraction coefficients-have been determined by minimization of atomic self-consistent field ground state energies. Advantages and necessary modifications of TZV basis sets are discussed for simple test calculations of molecular energies and nuclear magnetic resonance (NMR) chemical shieldings in treatments with and without inclusion of electron correlation.

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We present auxilliary basis sets for the atoms H to At ± excluding the Lanthanides ± optimized for an ecient treatment of molecular electronic Coulomb interactions. For atoms beyond Kr our approach is based on eective core potentials to describe core electrons. The approximate representation of the electron density in terms of the auxilliary basis has virtually no eect on computed structures and aects the energy by less than 10 À4 a.u. per atom. Eciency is demonstrated in applications for molecules with up to 300 atoms and 2500 basis functions.

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