Additional diffuse functions in basis sets for dipole-bound excited states of anions

Abstract

The existence of dipole-bound excited states has largely been shown by previous computation through the use of the standard LCAO-MO creation with numerous and diffuse atom-centered functions. Earlier work has suggested that the standard aug-cc-pVDZ basis set augmented with a small set of diffuse Rydberg-like orbitals is sufficient for the computation of dipole-bound ground states in anions. In this work, we explore the addition of four, even-tempered s-type functions augmenting the aug-cc-pVDZ set for the computation of dipole-bound excited states. It is shown herein that the inclusion of these orbitals is more cost-effective and internally accurate than atom-centered functions. Both vertical and adiabatic excitation energies are negligibly affected by the centering location of these additional diffuse functions. However, the excited state harmonic vibrational frequencies can be influenced by the placement of these additional diffuse functions, especially for the lowest energy modes.