Dear Community,

I used Forcite module to simulate the all-atom model, which includes positively charged polymer chain, hydroxide and water. Then, using the script TrajectoryCoarseGrainer, the full-atom trajectory file is transformed into coarse-grained trajectory file, and the force field information is obtained by using BoltzmannInversion script.

I used the Coarse Grainer/motion groups function to transform the all atomic polymer chain into coarse grained molecular chain, and defined water beads and hydroxide beads at the same time, and used them as the components of the template to build the box.

After geometry optimization, I ran dynamics （100ps NPT）, in which the time step was 0.1fs, because it always reported errors and needed to reduce the temperature and time step.

I found the density changed from 1g/cm3 to 300g/cm3.This is obviously unreasonable.

Why is this happening? How to solve it?

Thanks in advance.