LAMMPS is a GiD-problemtype that wraps the LAMMPS classical molecular dynamics (see lammps.sandia.gov)
GUI for some general data and postprocess animation of a result:
Download here LAMMPS-0.2-win-32.zip module and unzip it inside the /problemtypes GiD folder, Then you can load it in GiD from the menu Data->Problemtype->LAMMPS
This version includes LAMMPS compiled for Windows x32. The same version will work on Windows x64, must simply copy the contents of LAMMPS.gid\bin\win-x32 to LAMMPS.gid\bin\win-x64
For Linux platform must add the appropiated binaries to LAMMPS.gid\bin\linux-xx