[lammps-users] question about pair_coeffs

Hi,
I have a question about the pair_coeffs. I have been using lj/cut as pair_style for all my simulations. the pair_coeffs is as shown below-

epsilon = 1.0
sigma = 1.0
cut-off = 1.5

If I want to make the system more attractive, I would change the epsilon to a higher value. Right? Does the epsilon value imply the well depth. The reason I’m sasking this question is because, I understand that the well depth is not same as the epsilon value for a truncated & shifted L-J potential. Is this the case with lj/cut or does the epsilon and the well depth value imply the same for this particular pair_style?

Any explanation would be greatly appreciated.
Thank you
Venkat

Venkat,

If you're using lj/cut with the default "pair_modify
shift no", then epsilon is the well depth. So yes, a
larger epsilon would make the system more attractive.
You could also make the system more attractive by
using a larger cutoff.

If you use "pair_modify shift yes", then epsilon is no
longer the well depth. The entire potential curve is
shifted upward so that the potential is zero at the
cutoff. The shift is typically small (with a
reasonably large cutoff), so epsilon is typically
still almost equal to the well depth. See:
http://www.cs.sandia.gov/~sjplimp/lammps/doc/pair_modify.html

Paul

--- Venkat Padmanabhan <[email protected]>
wrote:

Hi,
I have a question about the pair_coeffs. I have been
using lj/cut as pair_style for all my simulations.
the pair_coeffs is as shown below-

epsilon = 1.0
sigma = 1.0
cut-off = 1.5

If I want to make the system more attractive, I
would change the epsilon to a higher value. Right?
Does the epsilon value imply the well depth. The
reason I'm sasking this question is because, I
understand that the well depth is not same as the
epsilon value for a truncated & shifted L-J
potential. Is this the case with lj/cut or does the
epsilon and the well depth value imply the same for
this particular pair_style?

Any explanation would be greatly appreciated.
Thank you
Venkat

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