Clusters of 13–150 Lennard-Jones atoms have been investigated, with attention given to clusters at both ‘magic’ and intermediate nuclearities. Icosahedral, decahedral and face-centred-cubic structures are compared in terms of their relative energies and the topology of the potential-energy surfaces. In particular, both gradient and second-derivative optimisation schemes are employed, and all structures are characterised in terms of their force constants. We find a number of interesting relationships between the three principal structural morphologies. Different capping routes are also compared to investigate possible growth schemes for the clusters of intermediate size. We find that the presence or absence of particular capping or surface atoms can be crucial in determining structural stability, showing that even this simple model potential can provide insights into the chemistry of small metal particles, as observed from experiment.