Date of this Version
New Journal of Physics 16 (2014) 028001
The shape resonances computed in the title paper are shown to be approximately 1.8 eV too high.
Garcia-Sanz et al  describe electron scattering calculations on anthracene in the gas phase and report the energies of seven temporary negative ion states, i.e. shape resonances, associated with electron attachment into the normally unoccupied π* molecular orbitals. The calculations were carried out at the ground state geometry of the neutral molecule, and thus the resonance energies represent the vertical attachment energies (VAEs) of the neutral. The purpose of this comment is to point out that their energies do not agree well with experiment  or with energies obtained from semi-empirical scalings of computed virtual orbital energies (VOEs), an approach that has been extensively and successfully used to identify resonances and their symmetries for a number of years. The energies of  lie too high by approximately 1.8 eV.