[lammps-users] pair_modify trouble in 2 polymer chain systems

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1

Hi all,

I am running a 2 different polymer chains system, one attractive
another repulisive. The program runs well when using explicit
pair_coeff for 1 1, 2 2, and 1 2. But, when I use pair_modify, this
causes FENE bonds become too far apart.

This works well:

pair_style lj/cut 2.5
pair_coeff 1 1 1.0 1.0 1.12
pair_coeff 2 2 4.0 1.0 2.5
pair_coeff 1 2 2.0 1.0 1.12 ( use Lorentz-Berthelot here for
epsilon, sigma).

But This DOES NOT:

pair_style lj/cut 2.5
pair_coeff 1 1 1.0 1.0 1.12
pair_coeff 2 2 4.0 1.0 2.5
pair_modify shift yes mix geometric (This does not work
with/without 'mix geometric' which is default though).

Any help, I have to use shifted LJ for the model.

Thanks,
Monojoy

2

Shifting and mixing are independent settings, so I'm not clear
on what you mean by it doesn't work. If you do different
kinds of mixing (auto or explicit, geometric vs arithmetic, etc)
then you are changing your model, so not clear why
you would expect the same results?

Steve

3

Hi Steve,

Well, it was my bad, did not define pair_style between 1 2, therefore,
it was not working. Anyway, now it works perfect. Also, as you said
earlier, I had to properly equilibrate which I wasn't doing wrong
before. Thanks for your help.

Yes, shifting and mixing are independent settings, both come through
pair_modify though.

Thanks,

Monojoy