Vertical detachment energy and adiabatic electron affinity have been calculated for small carbon clusters C. (n = 2-20), both for linear and monocyclic structures, in the framework of DFT formalism using the hybrid B3LYP functional with a basis set 6-31G* augmented of p diffuse functions, A good reproduction of experimental electron affinities has been obtained in that way for linear chains with n = 5-20 especially for odd members of the series. Results are poorer for monocyclic structures however experimental trends are reproduced. For both structures the lowest estimated fragmentation energy corresponding to the loss of C-3 remains larger than electron affinities for the sizes considered.