A Comparison of Density Functional and Coupled-Cluster Theories for the Equilibrium Properties of Valence Excited Electronic States: Spectroscopic Constants of Diatomics

The reliability of density functional theory and other electronic structure methods is examined for anharmonicities and spectroscopic constants of low-lying valence electronic excited states. the equilibrium bond length re, harmonic vibrational frequency ωe, rotational constant be, centrifugal distortion constant d(bar)e , and vibration-rotation interaction constant αe, have been determined for low-lying singlet excited states of bf, co, n2, ch+, and no+ . predictions using configuration interaction singles, equation-of-motion coupled-cluster singles and doubles, and various time-dependent density functional methods have been made using the 6-31g*, aug-cc-pvdz, and aug-cc-pvtz basis sets and compared to experimental values. time- dependent density functional theory compares favorably to equation-of-motion coupled-cluster theory for the properties considered, but errors are substantially larger for excited states than for ground states.