I had set up an MD simulation of my protein of interest using NAMD, along with water (TIP3P) PEG tetramer was also filled in the box at a concentration of 200mg/ml. Minimisation for 10000 steps using steepest descent followed by an equilibration for 1ns was performed. Following observations were made -

1. Box volume expanded by 1000 times

2. PEG molecules came together and formed aggregates/micelles

I have included ether parameters as suggested by some papers for this simulation.

Can anyone suggest the possible changes to be made to avoid these oucomes?