One of the major questions in astronomy is how stars form. Observations indicate that the vast majority of stars appear to form in groups or clusters from dozens to hundreds of thousands of stars. Therefore, to understand star formation, we need to understand how star clusters form. Ultimately this requires following a large set of physical processes including hydrodynamics, magnetic fields, radiation feedback from massive stars, and, to date, no simulation can treat the process in its full complexity. The contribution of this project is to understand the dynamics of stars during the formation of star clusters, and how the stellar population is shaped through stellar encounters before star formation stops in the parent region. To date, all N-body studies have been focused on the evolution of already formed star clusters, while standard star formation simulations can not accurately follow the dynamical interaction between stars, since they normally focus their efforts on the dynamics of the gas. In this project, we will perform a large set of N-body simulations using a modified version of the GPU-optimized code Nbody6, focusing on the formation of very massive star clusters (10^5 stars). These simulations are impossible to run in few core computers, and still challenging on dozens or hundreds of CPUs. GPU optimization makes this work viable and the aim of this request is to run the simulations of the largest clusters in our study. Given the unique approach of this project, these will be the largest simulations of star forming clusters, including hydrodynamical studies.