SHOULD THE STANDARD BASIS-SETS BE AUGMENTED WITH DIFFUSE FUNCTIONS ONHYDROGENS TO PROVIDE A REASONABLE DESCRIPTION OF THE LOWEST RYDBERG STATE OF HYDROGEN-CONTAINING MOLECULES

Augmentation of the standard basis sets with the diffuse functions, wh ich were optimized for non-Rydberg anions on the heavy atoms only, may not be adequate for calculating Rydberg states of molecules. Addition of diffuse functions on the hydrogens to such a basis set used for ca lculations of Rydberg states of hydrogen-containing species can make u p for this deficiency and lead to a reasonable description. This gives the possibility of using the standard basis sets (e.g., the 6-31G(d,p ) and 6-311G(d,p) basis sets) augmented by diffuse functions, both on the heavy atoms and on the hydrogen atoms, for these calculations and, therefore, provides an alternative to optimizing diffuse functions sp ecifically to describe Rydberg orbitals. Inclusion of diffuse s functi ons on hydrogens is less important in calculations of non-Rydberg hydr ogen-containing anions.