Hi, everyone
I am simulating a gas system at closed environment. So I use “fix wall/colloid or wall/lj126” to encompass the boundaries of the box. By using it, these gas molecules are running within the walls. However, the gas’s temperature and the system’s total energy are increasing with the time. I cannot understand it, because I use fix nve to all the atoms and I think the interaction between gas molecules and walls is elastic. I also find that the temperature is increasing more quickly by using “fix wall/lj126” than by using “fix wall/colloid”. So, where do I have a mistake?
Thank you very much ^ ^
Best regards
Kai
2011/8/13 Kai Zhong <[email protected]...>:
Hi, everyone
I am simulating a gas system at closed environment. So I use "fix
wall/colloid or wall/lj126" to encompass the boundaries of the box. By using
it, these gas molecules are running within the walls. However, the gas's
temperature and the system's total energy are increasing with the time. I
this increase of the kinetic energy is a consequence of the discretization
of time in an MD simulation and it cannot be avoided. every time a particle
runs into a wall, it will run up too high due to using finite time steps and
thus its potential energy increases which will be converted into kinetic
energy as soon as the particle bounces back. all you can do is to reduce
this error by using a shorter time step or counter it by applying a thermostat.
cannot understand it, because I use fix nve to all the atoms and I think the
interaction between gas molecules and walls is elastic. I also find that the
temperature is increasing more quickly by using "fix wall/lj126" than by
using "fix wall/colloid". So, where do I have a mistake?
the steeper the wall, the larger the aforementioned error.
you may want to try using a reflective wall instead.
axel.