[lammps-users] bjerrum length and dielectric constant

Dear,
I want to ask you a technical question about coulomb interaction in LAMMPS. in manual the coulomb potential is given by E = Cqiqj/epsilonr , but I want to use bjerrum length (e^2/(4piepsilonkb*T)) as system parameter. How can I deal with it. May I use other command to relate two?
Which command? Is there other methods.

I am looking forward to your reply, Thanks for your kindly consideration.

Ask Mark Stevens (msteve at sandia.gov), who's modeled polyelectrolytes
with LAMMPS and had to worry about the Bjerrum length.

Steve

2008/1/25 田文德 <[email protected]>:

Hi Wende,

You can derive the coulomb potential in terms of Bjerrum length and that would be E = kb T * lb qi qj / rij. Bjerrum length is equal to e^2/(dielectric constant * kb *T). So in Lammps, if you have implicit solvent, you can use PPPM and use the dielectric command to set the Bjerrum length of your system. If you are using coarse grain model with reduced units and set kbT = 1, then the Bjerrum length is the reciprocal of the dielectric constant. (lb = 1/dielectric constant)

In Lammps, I usually have the following lines in my input script for slab simulations

units lj
atom_type full
dimension 3
neighbor 0.5 bin
neigh_modify every 1 delay 3 check yes
boundary p p f
kspace_style pppm 0.0001
kspace_modify slab 3.0
dielectric 1.0

read_data sample.dat



and so on…

Jan-Michael