
Gromacs oplsp force field 
=========================

This is an extension of the opls-aa force field included in the Gromacs distribution. 
The force field includes monomers that can be used to model synthetic organic
block-co-polymers - in the same way as bio-polymers, i.e., peptides. 
The partial charges on the monomers were calculated as ESP charges with Gamess-US. 
The VdW parameters and bonded energy terms were taken from the opls-aa forcefield. 
Terms that were not defined explicitely in the original OPLS-AA force field were taken 
from terms including similar atom types. 
ffoplsp has been tested with GMX versions 3.1.4 and 4.0.7.

For installation all the files in the top directory need to be copied to the
Gromacs "top" directory (e.g. "/usr/local/share/gromcas/top") and the file FF.dat 
therein should be modified to include the new force field (and example FF.dat is 
included in top/). that's it.
The polymer directory contains various short polymers that can be used as templates 
for building different and/or longer ones.

Monomers included are:
* benzyl-methacrylate
* butyl-acrylate
* butyl-methacrylate
* hexyl-methacrylate
* methyl-methacrylate
* styrene
* styrene modified (extended back bone)

for each monomer there's three residues types
 1 M-terminal 
 2 H-terminal
 3 evrything in between

as in:

       S       S       S
       |       |       |
 CH3 - C - C - C - C - C - H
[       ] [     ] [         ]


this is similar to the amber force field for proteins which includes
extra resiues for C and N termini.

for example styrene has the three residue names:
STM ... M-terminus
STN ... in between
STB ... H-terminus

In principle every possible combination of monomers, with arbitrary lengths
of fragments, can be modeled. The only limitation is that they have to have the 
correct residue and atom names and atom order. I used Accelrys polymer builder 
to make the actual coordinates. It should be straigth forward though to replace 
this with some simple script that takes monomer uits as input, to produce the 
coordinates of polymers. If people show any interest in this forcefield I might 
make that myself and include it into this distribution. For a start you can use 
one of the short polymers that are included here, and modify/extend them in a 
text editor.

for questions and comments contact me:
michael.brunsteiner@tugraz.at or mbx0009@yahoo.com
