# fix wall/reflect

I am using fix wall/reflect in z direction by specifying zlow and zhigh. And I am using NPT ensemble by applying barostat in two directions x and y.

fix 4 all npt temp 300 3000 1.0 x 0.0 0.0 1.0 y 0.0 0.0 1.0 couple xy

But I find pressure increases with the time steps and is not averaged out to zero.

Is there any method to reduce pressure.

I am using fix wall/reflect in z direction by specifying zlow and zhigh. And
I am using NPT ensemble by applying barostat in two directions x and y.

fix 4 all npt temp 300 3000 1.0 x 0.0 0.0 1.0 y 0.0 0.0 1.0 couple xy

But I find pressure increases with the time steps and is not averaged out to
zero.
Is there any method to reduce pressure.

wrong question. try: why *does* the pressure increase?
there must be something *else* in your input that causes that your
system to be off its equilibrium.

axel.

As I am increasing the temperature, the sample tries to expand. But the use of fix wall/reflect prevents the box from expanding in Z direction and hence pressure builds up.

If I use periodic boundary condition in all direction and no fix wall then pressure is averaged out to zero.

Its because of fix wall pressure is piling up. How to prevent that pressure from piling up