[lammps-users] special bonds!

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1

Dear users,

I am a new user to lammps. We want to simulate a polymer melt.
Could any one explain the use of “special bonds” command? In which
situations it is useful.

Thanks
Gerald

2

2008/5/7 Smith Gerald <gerald88@…762…>:

Dear users,

I am a new user to lammps. We want to simulate a polymer melt.
Could any one explain the use of “special bonds” command? In which
situations it is useful.

Gerald:

The special bonds command is used to avoid “double counting” of Coulombic and pairwse interactions in molecules, as many force fields take interactions between nearest neighbors (1-2), between next-nearest neighbors (1-3), and between 1-4 atoms into account when parameterizing the various bond, angle, and dihedral terms.

Special_bonds coefficients for the CHARMM and AMBER force fields already are specified within LAMMPS; other combinations should be used as directed by the force field you are using.

–AEI

3

Dear users,

I am a new user to lammps. We want to simulate a polymer melt.
Could any one explain the use of "special bonds" command? In which
situations it is useful.

gerald,

this option is needed whenever the force field requires it.
typically all-atom and similar force fields use this so you can
parameterize bonded and non-bonded interactions independently
(well, it becomes "extra special" with dihedrals).

cheers,
   axel.

4

Special bonds turns off pairwise interactions between 2 atoms
that are bonded to each other. That's 1-2. Similar for 1-3 and 1-4
interactions within an angle or dihedral.

Steve

5

Thank you all. It really helped me.