  We present a method (the Aufbau/Abbau method) for optimizing the structure of
a whole series of clusters without making any assumptions on the structure.
Subsequently, the method is combined with the embedded-atom method in
determining the structure of the two energetically lowest isomers of Ni_N
clusters with N up to 150. Finally, various analytical descriptors are
introduced that are used in studying the overall shape of the clusters, their
structure and stability, and possible growth and dissociation processes.
