Charmm2lammps

Charmm2lammps.pl is a useful little code which takes in forcefield [top/par], psf and pdb files in Charmm format and converts them to Lammps data and sample input file. This is extremely useful for running simulations in the much better written MD code, LAMMPS. While trying to simulate a polymer chain I came across a very interesting feature in charmm2lammps; it really expects the force constant in the forcefield parameter file to be non-zero. This works just fine when you never want to specify angle/dihedral parameters to free chains. But when you want to control the parameters in between runs, it is a good idea to define all the angle and dihedrals and then decide to turn them off/on in LAMMPS by setting the force constant to 0/nonzero.