  The induced surface charges appear to diverge when dielectric particles form
close contacts. Resolving this singularity numerically is prohibitively
expensive because high spatial resolution is needed. We show that the strength
of this singularity is logarithmic in both inter-particle separation and
dielectric permittivity. A regularization scheme is proposed to isolate this
singularity, and to calculate the exact cohesive energy for clusters of
contacting dielectric particles. The results indicate that polarization energy
stabilizes clusters of open configurations when permittivity is high, in
agreement with the behavior of conducting particles, but stabilizes the compact
configurations when permittivity is low.
