Minimum image convection

When periodic boundary conditions are used, the system must be large enough for particles with their own images. For non-charged systems, this is accomplished by having the simulated box be larger than twice the Lennard-Jones potential cutoff. Each atom experiences then at most 

The minimum image convention (Fig. 14.4) is used to ensure that a particle interacts with another particle or only one of its images, whichever is closest. A piece of FORTRAN code for computing the potential energy of a system with A particles interacting with a simple Lennard-Jones potential is as follows  

ULJ = 4 epsilon (srij + srij 2) c End do-loop over j particles enddo 

In the previous code, the first value for i is / = 1 and according to the figure positions  

The closest image of particle 2 to particle 1 is the one inside the main cell. The minimum image convention will then give the same distances as before. 

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