Atomistic simulations of single crystal silicon cubic box containing nano-sized voids under hydrostatic tension are investigated by using three-dimensional strain-controlled molecular dynamics method.The results show that the failure of the cubes may be initiated either by brittle cleavage on void surface or by ductile void coalescence in the inter-void ligament.By varying the inter-void ligament distance of the models,we investigated fracture mechanisms which determine the two fracture behaviors.A critical initial inter-void ligament distance is suggested to be the transition criterion for each model with certain void size.Further analysis reveals the void growth and interaction mechanism that determines whether the initial fracture behaviors will be in brittle or ductile manner.It also indicates the remarkable interaction between voids characterized by voids coalescence in single crystal silicon as a result of vacancy diffusion in the ligament triggered by void surfaces and dislocation emission surrounding the voids.