Computed electron removal energies for CuN- clusters, N=9-20, are presented for the three lowest-energy isomers obtained from extensive, unbiased searches for the minimum energy structure at each size. The density functional theory (DFT) computations make use of a scheme introduced by Jellinek and Acioli (JA) [J. Chem. Phys. 118, 7783 (2003)] that obtains electron removal energies from DFT orbital energies using corrections based on DFT total energies. The computed removal energies are compared with the measured photoelectron spectra (PES) for CuN-. The patterns of computed removal energies are shown to be isomer specific for clusters in this size range. By matching the computed removal energies to the observed PES, the isomers responsible for the PES are identified. The results of the JA scheme are compared to those obtained using other DFT-based methods.