We apply a finite-difference pseudopotential density functional theory in real space and the Langevin molecular dynamics annealing technique as well as the adiabatic time-dependent density functional theory within the local density approximation (TDLDA) to the descriptions of structures and optical absorption spectra of carbon clusters C-8. It is shown that the odd-numbered clusters have the linear structures and most of the even-numbered clusters prefer cyclic structures. The calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations. (C) 2003 Elsevier B.V. All rights reserved.