Density functional calculation are performed to study T8C12 isomers (T-d, C-3v, and D-2d) in the neutral, cationic, and anionic charge states. C-3v symmetry is found to be the most stable geometry for the neutral and anion, and the C-3v and D-2d isomers to be quasi-iso-energetic lowest for the cation. The electronic structure analysis show that d electron tends to be localized in the ground state. The theoretical assignment for the features in the experimental photoelectron spectra is given. All results obtained are in good agreement with the available experimental data and indicate that the C-3v and D-2d isomers may coexist in the photoelectron spectroscopy experiment. (C) 2004 American Institute of Physics.