Shifted forces in molecular dynamics

Simulations involving the Lennard-Jones potential usually employ a cut-off at $r=2.5σ$. This paper investigates the possibility of reducing the cut-off. Two different cut-off implementations are compared, the standard shifted potential cut-off and the less commonly used shifted forces cut-off. The first has correct forces below the cut-off, whereas the shifted forces cut-off modifies Newton's equations at all distances. The latter is nevertheless superior; we find that for most purposes realistic simulations may be obtained using a shifted-forces cut-off at $r=1.5σ$, even though the pair force is here 30 times larger than at $r=2.5σ$.

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