The utility WATERADD adds water from an equilibrated configuration of 256 SPC water molecules at 300 K to fill out the MD cell. The utility SOLVADD fills out the MD box with single-site solvent molecules from a f.c.c lattice. The FIELD files will then need to be edited to account for the solvent molecules added to the file.
Hint: to save yourself some work in entering the non-bonded interactions variables involving solvent sites to the FIELD file put two bogus atoms of each solvent type at the end of the CONNECT_DAT file (for AMBER force-fields) the utility AMBFORCE will then evaluate all the non-bonded variables required by DL_POLY_2 . Remember to delete the bogus entries from the CONFIG file before running DL_POLY_2 .