of order 9.9 eV. These values are of the same order of magnitude for larger chains. According to the linear geometry of the chain, the optical response shows a dominant resonance peak along the longitudinal direction at a frequency of 6.4 eV. The transverse modes are suppressed by at least one order of magnitude (mind that transverse strengths have been multiplied by a factor of 20 to allow a better graphical comparison with the longitudinal modes) and are significantly fragmented. There are three main peaks : one at the same energy as the longitudinal plasmon peak, and two other ones at higher energies near the IP energy. The all dominant longitudinal mode lies well below the IP, a feature common to all carbon chains. Associated time scales are now typically ranging from sub-fs to fs. Ionic vibration energies lie again in the 0.15 eV range with associated time scales of order 27.6 fs.

We finally discuss the case of the prototypical water molecule H$_2$O (lower right block) which has 8 active valence electrons in our calculations (6 for O and 1 per each H). The s.p. energy span is now with 16 eV even larger than in C$_{60}$, in spite 