Investigating thermodynamic properties of liquid-solid transitions of
flexible homopolymers with elastic bonds by means of multicanonical Monte Carlo
simulations, we find crystalline conformations that resemble ground-state
structures of Lennard-Jones clusters. This allows us to set up a structural
classification scheme for finite-length flexible polymers and their freezing
mechanism in analogy to atomic cluster formation. Crystals of polymers with
"magic length" turn out to be perfectly icosahedral