Gaussian Basis Sets for High - Quality ab Initio Calculations 3029

Different types of Gaussian basis sets for accurate LCAO calculations are discussed. For calculations designed to recover a substantial portion of the correlation energy, we suggest the use of basis sets comprising natural orbitals from correlated calculations on the atoms. These basis sets have proven to be very efficient in accounting for large fractions of the molecular correlation energy. For cases in which an SCF or MCSCF treatment is adequate the use of a floating basis provides a rapid convergence to the large-basis limit.