Role of NPzT Simulations

Why use in NPzT ensemble?

When the dimensions of channel goes to dimensions where the effect of walls is very dominant and density inside the channel is no longer equal to bulk density. In such a case, if we fill the channel with bulk density, it will increase the pressure. It becomes essential to use a pressure control method in such cases. To avoid any discrepancy in the simulations, we should provide the optimum number of water molecules. 

How to implement NPzT simulation?

Fix one wall of the channel and fill the channel with estimated number of fluid molecules. Keep the other wall of the channel flexible. Put pressure on the flexible wall equal to ensemble pressure (typically 1 atm) and let the system equilibrate. When the internal pressure of the channel becomes equal to the applied pressure, wall will become stable at that position. Keep the system periodic in other two directions.

This will give you optimum height for a given number of fluid (water/ polymer) molecules.