CCL: DL_POLY error message "1-4 separation ..."

["Bill Smith" <w.smith##dl.ac.uk>]

 Sent to CCL by: "Bill  Smith" [w.smith---dl.ac.uk]
 The error concerning the 1-4 distance exceeding the cutoff distance arises
 because you have specified a dihedral potential in which the atoms in the 1 and
 4 positions have separated to a distance larger than the van der waals cut-off
 that is applied to pair forces.
 This creates a problem for the routine that calculates the dihedral force, which
 needs to calculate a 1-4 interaction, but there is no reference to the required
 force in the bookkeeping arrays and no associated interpolation values in the
 potential and force tables, which are constructed using the defined cut-off. It
 is generally not safe simply to assume the 1-4 term is zero at this distance.
 The problem arises in a simulation for two common reasons: the cut-off specified
 is too short to allow for the 1-4 term in a `stretched' molecule; or the
 parameters used to define the bonds, bond angles and dihedrals are incorrect or
 possibly too `soft' and have allowed the molecule to assume an improbable
 structure.
 A third possibility is that the simulation is wildly unstable and is pushing the
 structure to extremes. There should be other symptoms here - like high
 temperatures and high configuration energies. The integration algorithm may also
 show instability - large energy fluctuations for example.
 If your cut-off is large (> 10A say) then you should check that the force
 field has been correctly defined.