A model of three-dimensional quantum chaotic billiards is used to inve
stigate global quantum fluctuations in metallic particles. The quantum
system is described by means of a tight-binding Hamiltonian in which
the energies of the orbitals at the surface sites are chosen at random
in the range (-W/2,W/2). The results indicate that for reasonable val
ues of W (on the order of half the bandwidth) the energy fluctuations
of the highest occupied level are much larger than the corresponding a
verage interlevel spacing. This provides a natural explanation for aut
oionization effects in granular metals.