Guide to using polyphosphate parameters:

We have recently parameterized di- and tri- phosphate tails for use with the
AMBER95 force field.  The parameters are based on reproduction of RHF/6-31+G*
potential surface.  Methyldiphosphate and methyltriphosphate were used as model
compounds.  To most accurately mode the behavior of the polyphosphates an
additional atom type for the terminal anionic oxygens, O3, was added.  The RESP
methodology was used to assign partial charges.

ADP.prep, ATP.prep
- AMBER6 prep files for ADP and ATP.  RESP partial charges are given in the
  last column.
- Atom names (ie: C4*, PB, O3G) must match the atom names as given in the pdb.

frcmod.phosphate
- Need to copy the leaprc file to your working directory and modify it to
  contain the O3 atom type.

        { "O"   "O" "sp2" }
        { "O3"  "O" "sp2" }
        { "O2"  "O" "sp2" }
        { "OW"  "O" "sp3" }