Hello,
I’m performing NPT simulations in LAMMPS with periodic boundary conditions and investigating the dependence of my results on the two-body potential cutoff radius. Initially, I ensured the cutoff was always smaller than half the smallest box dimension to comply with the minimum image convention. However, I accidentally ran simulations with a cutoff larger than half the box length, and surprisingly for my LAMMPS did not throw any errors. Also, the results appeared physically reasonable (not nonsense).
Upon researching this, I found some old discussions (2009–2010) with conflicting comments on whether cutoffs can exceed half the box size (e.g., this thread). Additionally, the LAMMPS Developer Communication Guide states:
Force computation in LAMMPS is not subject to minimum image conventions and thus cutoffs may be larger than half the simulation domain.
As a beginner, I’m confused by this and would appreciate clarification on:
- Can the cutoff radius indeed be arbitrarily large without causing calculation errors (e.g., due to unphysical self-interactions)?
- How does LAMMPS avoid infinite self-interactions with periodic images when the cutoff exceeds half the box size?
Thank you for your insights!