We show that new aspects of the physics of microclusters can be investigated accurately with ab initio molecular dynamics. We present results on a number of properties of SiN aggregates (N up to 10) at both zero and finite temperatures. The results of dynamical simulated annealing for the ground state point to a complex growth sequence. Simulations at finite temperatures show the existence of two regimes, solidlike and liquidlike, with substantially different electronic and structural properties. © 1988 The American Physical Society.