parameters of DPD in units lj

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1

Dear LAMMPS users,

I’m a little confused about parametrization of LAMMPS DPD. Now, I’m trying to reproduce the previous study obtained by DPD. They performed ordinary DPD, that is, m=rc=kBT=1, sigma=3 and gamma=4.5. And aii is 104. aijs were converted by aij = aii + 3.27xij. They introduced harmonic bond potential between polymer beads. Force constant and rs are 100 and 0.86, respectively. When I try to calculate such system, can I use those parameters without change?

For example,

units lj

pair_style dpd 1.0 1.0 123456

pair_coeff 1 1 104.0 4.5

bond_style harmonic

bond_coeff 1 50.0 0.86

According to LAMMPS manual, “units lj” is unitless but all units are reduced by epsilon and/or sigma. In my DPD calculation, all epsilon and sigma (in lj units, not DPD’s) can be ignored as 1?

I attached my input file. I would appreciate it if you would give me some advice.

I took mistake when I post, please ignore my previous post.

in.DPD_Naf (765 Bytes)

2

The params you listed from the paper sound like they are unitless,

i.e. LJ units. Except maybe the bond K of 100 which seems

large for LJ units. However it is possible they are just trying

to have a stiff bond so that the soft DPD particles do not

get too far apart. Bond crossing (between 2 different chains)

is a problem for DPD b/c of the soft particles. There is a pair srd

option in LAMMPS to prevent bond crossings in DPD chains,

so you can look at that as well.

Steve

3

Dear Steve,

Thank you for your reply and kind advices.
I read LAMMPS manuals but I couldn’t find out “pair_style srd” option which you recommended. Is it a mistype of “pair_style srp”?

Hironori Sakai

4

yes. style srp

Steve