CHARMM 19 1-4 interactions and special_bonds

I’m using the CHARMM19 force field. In the parameter set, it appears to set the 1-4 electrostatic interactions to 0.4 of the normal interaction. I’m looking at this line in the parameter set:

CUTNB 8.0 CTOFNB 7.5 CTONNB 6.5 EPS 1.0 E14FAC 0.4 WMIN 1.5

Should this be set using the special_bonds command? Specifically, something like:

special_bonds lj/coul 0.0 0.0 0.4

Thanks for the help.

I'm using the CHARMM19 force field. In the parameter set, it appears to set
the 1-4 electrostatic interactions to 0.4 of the normal interaction. I'm
looking at this line in the parameter set:

CUTNB 8\.0  CTOFNB 7\.5  CTONNB 6\.5  EPS 1\.0  E14FAC 0\.4  WMIN 1\.5

Should this be set using the special_bonds command? Specifically, something
like:

special\_bonds lj/coul 0\.0 0\.0 0\.4

1-4 parameters for charmm require the use of a special pair style,
since there can be overrides of the global scaling. for details, please see:

http://lammps.sandia.gov/doc/pair_charmm.html
http://lammps.sandia.gov/doc/special_bonds.html

axel.

Hi Axel,

I’m using the pair_style lj/charmm/coul/long and the dihedral_style charmm. In the charmm dihedral style there is a weighting factor, so I guess my actual question is, do I set the weighting factor to 0.4 or do I use the special_bonds?

Again, thanks for the help.

Hi Axel,

I'm using the pair_style lj/charmm/coul/long and the dihedral_style charmm.
In the charmm dihedral style there is a weighting factor, so I guess my
actual question is, do I set the weighting factor to 0.4 or do I use the
special_bonds?

the documentation is very clear on that.
you don't use special_bonds. they should
be set to "charmm"

axel.

Great! I did set the special_bonds to charmm and set the weighting factor in the dihedral_style to 0.4 for the simulation. I just wanted to make sure my understanding was correct.