Ab initio molecular dynamics simulations of negatively charged clusters of 2 to 48 ammonia molecules were
performed to elucidate the electronic stability of the excess electron as a function of cluster size. We show that
while the electronic stability of finite temperature clusters increases with cluster size, as few as 5-7 ammonia
molecules can bind an excess electron, reaching a VBE slightly less than half of the bulk value for the largest
system studied. These results, which are in agreement with previous studies wherever available, allowed us
to analyze the excess electron binding patterns in terms of its radius of gyration and shape anisotropy and
provide a qualitative interpretation based on a particle-in-a-spherical-well model.