Atomistic simulations are performed for the study of defect nucleation and evolution in A1 single crystal under nanoinclentation. Methodologies employed include the molecular dynamics and molecular mechanics simulations with embedded-atom potentials. Simulated is the indenting process on A1(111) surface with the spherical tip of indenter. Using the visualization technique of centrosymmetry parameters, homogeneous nucleations and early evolutions of dislocations are investigated for deepening our understanding of incipient plasticity at the atomic scale. We have shown that the nucleation sites of initial dislocation loops vary with the empirical potentials chosen for the simulation. Identifications are also made for the continuously changing structures of dislocation locks underneath the indenter tip and for the glide of prismatic partial dislocation loops far away from the contact surface. (c) 2005 Elsevier Ltd. All rights reserved.