Cutoff

A cutoff is a finite distance after which some interaction (electrostatic or van der Waals) is truncated.  Cutoffs also apply to neighborlist updating.  Relevant .mdp parameters are rcoulomb, rvdw, and rlist.  Cutoff values are often specific for different force fields, and altering them may have negative consequences for your results.  Refer to the primary literature for your force field of choice for the recommended settings.

There are some exceptions to the above statement, as the results from some force fields are more tolerant of change.  For others, the requirements are more strict.  A common problem that new users encounter is that they haphazardly set cutoff values for which there is no discernible justification, and their system blows up as a result.  Note, too, that one must also satisfy the minimum image convention simultaneously; thus, systems have a minimum size requirement in many cases, and grompp will try to warn you when this happens.