problem with rigid body simulation

Hi everybody,

I am trying to simulate CO2 in bulk at NTP. I have considered CO2 as three atom rigid molecules. I use fix rigid to that. Now the problem I am facing is regarding the energies. The potential energies as well as total energies are positive. To check whether overlapping of molecules causes this problem I have tried to simulate putting only two molecules in the simulation box. Even in this case also the energies are positive. When I visualize the trajectory I do not see any overlapping of the two molecules. They stay far apart. Now I do not understand why it is like this. I am not able to figure out where I am going wrong. Can any body suggest or comment something which will help me to resolve the problem. I have posted the input script as well as as the data file for the two molecule case. Thanks in advance. (753 Bytes)

Are you excluding energy for atoms in the same molecule?
You can do this with neigh_modify exclude.