A classical, hybrid Monte Carlo-molecular dynamic (MC-MD) algorithm for the study of phenomena like two-dimensional (2D) island stability or step-edge evolution on semiconductor surfaces is introduced. The advantages of working off lattice and utilizing bulk-fitted potentials are also presented. It is based on the introduction of collective moves in the MC algorithm. The algorithm is used in the analysis of 2D Si islands on Si(001). The results on early stages of island stability, island formation versus system size and temperature and step-edge evolution are presented.