four examples of systems computed with the tools described in Secs. \[sec:theo\], \[sec:sic\_stat\] and \[sec:sic\_optresp\]. They cover several different binding types and properties.

![Four typical examples of molecules and clusters explored theoretically in this review, namely the metal cluster ${{\rm
      Na}_{41}}^+$ (upper left), the Buckminster fullerene C$_{60}$ (upper right), the carbon chain C$_5$ (lower left), and the covalent molecule H$_2$O (lower right). For each panel: Top row : ionic structures (all plotted at the same scale) and single particle energies of the valence electrons whose number is indicated; Bottom row : corresponding optical response. For C$_5$, the transverse spectrum is multiplied by 20 to ease the comparison with the longitudinal response. The vertical dashes indicate the position of the ionization potential in each case. \[fig:systems\]](fig1ter){width="0.92\linewidth"}

The figure shows single-particle (s.p.) energies, optical response and ionic structure. The four presented systems are ${{\rm Na}_{41}}^+$ as an example of a simple metal cluster, C$_{60}$ for its outstanding properties and many applications, H$_2$O as a prototype of a covalent molecule, and C$_5$ as a simple carbon chain, which displays interesting optical properties. Let us analyze each system separately to extract typical properties.

We start with the ${{\rm Na}_{41}}^+$ cluster (upper left block in 