  Electronic and optical properties of silver clusters were calculated using
two different \textit{ab initio} approaches: 1) based on all-electron
full-potential linearized-augmented plane-wave method and 2) local basis
function pseudopotential approach. Agreement is found between the two methods
for small and intermediate sized clusters for which the former method is
limited due to its all-electron formulation. The latter, due to non-periodic
boundary conditions, is the more natural approach to simulate small clusters.
The effect of cluster size is then explored using the local basis function
approach. We find that as the cluster size increases, the electronic structure
undergoes a transition from molecular behavior to nanoparticle behavior at a
cluster size of 140 atoms (diameter $\sim 1.7$\,nm). Above this cluster size
the step-like electronic structure, evident as several features in the
imaginary part of the polarizability of all clusters smaller than
Ag$_\mathrm{147}$, gives way to a dominant plasmon peak localized at
wavelengths 350\,nm$\le\lambda\le$ 600\,nm. It is, thus, at this length-scale
that the conduction electrons' collective oscillations that are responsible for
plasmonic resonances begin to dominate the opto-electronic properties of silver
nanoclusters.
