DL_POLY_2 checks when constructing the interpolation tables for the short ranged
potentials that the potential function requested is
one which is of a form known to the program. If the requested
potential form is unknown, termination of the program results.
The most probable cause of this is the incorrect choice of the potential
keyword in the FIELD file or one in the wrong columns (input is formatted).
Action:
Read the DL_POLY_2 documentation and find the potential keyword for the
potential desired. Insert the correct index in the FIELD file
definition and ensure it occurs in the correct columns (17-20).
If the correct form is not available, look at the
subroutine FORGEN (or its variant) and define the potential
for yourself. It is easily done.