We report the results of an extensive structural study of Na13, Mg13, Al13, and Si13 carried out with the Car-Parrinello method. Several and mostly unforeseen noncrystalline structures are discovered to characterize the low portion of the potential energy surface. Crystalline structures are shown either to correspond to high-energy local minima or to be highly unstable. The low-energy structural pattern appears to change significantly from one element to the other. Specific characteristics as well as trends are discussed. © 1992 American Institute of Physics.