  Efforts toward stabilization of the Si$_{20}$ fullerene through different
schemes have failed despite several theoretical predictions. However, recently
Tillmann {\it et. al.} succeeded to stabilize the Si$_{20}$ fullerene through
exohedral decoration with eight Cl substituents and twelve SiCl$_3$ groups on
the surface and enclosing Cl$^-$ ion. A deeper understanding on what factors
lead to stabilization will open the path for stabilizing other systems of
interest. Here, we employ the minima hopping method within density functional
theory to understand the potential energy surface. The study shows that the
exo-endo halide decoration of the cage alters the glassy nature of the
potential energy surface of pure cage to structure seeker. Further analysis of
different properties of the global minima, reveal that the extra electron
instead of residing on the central encapsulated atom in the cage, it is
distributed on the cage and increases the encapsulation energy; thereby
stabilizing the system. We also provide estimates of the stability for
different kind of exo-endo halide decorations and their feasible realization in
experiments.
