Species with negative electron affinity and standard DFT methodsElectronic supplementary information (ESI) available: (i) Details of calculations (total energies, zero point corrections, etc.) and correlations obtained with different basis sets. (ii) Color graphics: structure, dipole, SOMO diagram and spin densities. (iii) xyz coordinates of all species. See http://www.rsc.org/suppdata/cp/b4/b403898c/