Calculations of the non-bonded energies or forces are the most time consuming step in the simulation. To solve this dilemma, one of the most common and smart ways is to employ a non-bonded cut-off and to apply the minimum image convention. The further apart than cut-off values of all pair interactions are set to be zero. However, the cut-off radius ought to be not so large that the particles see their own mimics when periodic condition applied.