I'm running a simple DPD simulation of water molecules. I have 100*100*100 box with number density of 5 and aii= 15. When I run the simulations at the end of the calculations most of my particles are outside of the box. Is this just a visual thing due to PBC? if so, how can I keep the particles inside the box? I have also tried polymer chains with 50 repeating units, and they do stay inside the box.