Ambiguity of compute group/group

Hi researchers

I’m dealing with a mixture of water and hydrocarbons and want to calculate pair-wise energy and forces between water molecules as below:

compute 1 water group/group water pair yes

however, the thermo output prints zero force components!! but energy has a finite value.

thermo_style step c_1 c_1[1] c_1[2] c_1[3]

Why does go wrong in my work?

Hello Lu/Robert:

the result of the calculation depends on the force field that you use and on the initial geometry.


I use OPLS-AA and already double checked all parameters.

Also, the coulombic interaction energy between similarly signed atoms is negative!!

What is really wrong with my code?