  We report calculations of the ground state energies and geometries for
clusters of different sizes (up to 80 particles), where individual particles
interact simultaneously via a short-ranged attractive -modeled with a
generalization of the Lennard-Jones potential- and a long-ranged repulsive
Yukawa potential. We show that, for specific choices of the parameters of the
repulsive potential, the ground state energy per particle has a minimum at a
finite cluster size. For these values of the parameters in the thermodynamic
limit, at low temperatures and small packing fractions -where clustering is
favored and cluster-cluster interactions can be neglected- thermodynamically
stable cluster phases can be formed. The analysis of the ground state
geometries shows that the spherical shape is marginally stable. In the majority
of the studied cases, we find that, above a certain size, ground state clusters
preferentially grow almost in one dimension.
