# How to effectively simulate high density systems in GROMACS?

I have a system with a dense liquid solvent and a polymer solute. I have inserted all the molecules randomly using gmx insert-molecules and then did the energy minimization and equilibration steps to get to the required density. However as the solvent is so dense, there's no space for the movement of the polymer molecules over the course of the production simulation run. I have waited for upto 10ns but there barely seems to be a change. Is there a way to build such systems to observe change in properties with and without the solute in shorter periods of time? Should I consider smaller densities of solvent or higher concentrations of solute? If so, what is the criteria to match the properties like viscosity from the simulation with that of experimental properties that are performed at high densities and low concentrations of solute?

• Can you give us a temperature/image of a model? It may just be that your system is so viscous that nothing will happen over long periods of time. Dec 2 '20 at 12:03
• @TristanMaxson When experiments are performed on the same system at the same temperature of 298K and 350 bar, the viscosity improved significantly. But, it is not seen that way with this simulation. Added the images for reference. Dec 2 '20 at 13:06
• Have you considered metadynamics? Dec 2 '20 at 20:58
• Maybe increasing the solvent density in small steps can give you a clue about what is happening.
– Camps
Dec 11 '20 at 18:23
• KavyaMrudula: Have you had a chance to consider the suggestion by Camps? @MDSimulation Perhaps the user doesn't know what Metadynamics is. Perhaps you can could elaborate on why metadynamics would help? Feb 28 at 5:21