lammps-users Digest, Vol 107, Issue 30

Hi Shimiao,


I am using LAMMPS to study polymer network, in which bead-spring chain
model is applied. Recently I met a problem that I am not sure if it is
realistic to use LAMMPS pizza toolkit (chain tool) to build equilibrium
polymer melt containing long bead-spring chains (250~500 beads).

You can build your system using chain.f file which comes with the tools folder of Lammps. All you need to do is to compile your fortran file chain.f. And then use ./a.out < def.chain >
Where def.chain , is the parameters file of your melt (you can find an example in the tools directory)

previous experience dealt with short bead-spring FENE chains (10~30 beads),
in which I used the chain tool to construct some chains (1000~1500), and
minimize the system in LAMMPS and make it run for a few million steps
before turning on polymerization using fix bond/create. In this way the
polymer melt should have reached equilibrium state before reaction.
However, if the chains are very long, this simple method may not be
applicable as I have learned the relaxation time increases significantly
with chain length, but I am not sure.

In order to equilibrate melts there are couple of must read papers.
One of them is :
For me personally this paper was also very helpful:

You can read how I did equilibrate my melts in this blog entry (sorry blog is very much under development so it doesn’t look nice yet)
Its pretty much follows the algorithm suggested by Sliozberg(the second paper).

Good luck,