Sistem shifted.

Dear all,

I have a system of a fluid confined between two walls in which I apply a
pressure on them equal and oppossite. For doing that I am using the
aveforce command with a constant force applied in z after averaging. The
problem I am facing is that after 1-2 nanoseconds of simulation the
entire system is shifted upwards so my binning for averaging is useless
and also I loose atoms at some point. It's seems to be a problem with
floating point representation since -force != force slightly so when it
runs for long this difference propagates and does matter causing the
system to shift. Did someone face that before or a similar case and know
some trick to deal with that?. For now I am fixing one wall and applying
pressure in the other but that leads to some non-symetric behaviour in
the system which I would like to get rid of.

Thanks in advance,

Eduardo

- MSc student at Imperial College London

Dear all,

I have a system of a fluid confined between two walls in which I apply a
pressure on them equal and oppossite. For doing that I am using the
aveforce command with a constant force applied in z after averaging. The
problem I am facing is that after 1-2 nanoseconds of simulation the
entire system is shifted upwards so my binning for averaging is useless
and also I loose atoms at some point. It's seems to be a problem with
floating point representation since -force != force slightly so when it
runs for long this difference propagates and does matter causing the
system to shift. Did someone face that before or a similar case and know
some trick to deal with that?. For now I am fixing one wall and applying
pressure in the other but that leads to some non-symetric behaviour in
the system which I would like to get rid of.

how about defining an equal style variable that computes a weak
harmonic restoring force and add/subtract it to/from your two aveforce
fixes?

axel.

Oh, I guess that could work.

Thanks Axel.

Eduardo