Ion beam neutralization during operation of ion sources requires current coupling between beam ions and electrons from the neutralizer. The current and charge density equalization during neutralization is accomplished in practice, however, the exact process has not been adequately simulated/understood due to the wide range of conditions. In order to resolve the role of electrons in the beam neutralization process, full particle-in-cell (PIC) simulations are carried out using a high-fidelity electrostatic particle-in-cell code EUPIC1. In this talk we extend our previous work2-6 and present a broader view of ion beam neutralization process by electron emission. We consider an idealized 1 D configuration following a theoretical ion beam model7, where ions and electrons are injected from the same area into vacuum. Charge and current neutralization is assumed to take place at a certain distance downstream of the injection plane. The theoretical model includes dimensionless Beam Kinetic Energy (KEi) normalized by electron thermal energy (kTe) and predicts a dimensionless neutralization distance as a function of beam kinetic energy. Our simulation results demonstrates the current coupling of both fast and mesothermal ion beams as well as neutralization distances.