[lammps-users] Lj/cut pair_style

Dear all,

I want to use a lj/cut pair_style for two type of molecules,
let’s say A, B.

I would like to use a standard LJ potential for AA (with attractive part),
and a shifted & truncated LJ for AB and BB (strictly repulsive).
In my case also, I will also simulate systems with only one B
particle so that BB interactions will not take place.

Is it possible to do it with Lammps, or the ‘pair modify shift’
command will apply to all type of interactions? I would also
like to apply a tail correction for AA interactions, and I wonder
if this poses other problems.

Dear all,

I want to use a lj/cut pair_style for two type of molecules,
let's say A, B.

I would like to use a standard LJ potential for AA (with attractive
part),
and a shifted & truncated LJ for AB and BB (strictly repulsive).
In my case also, I will also simulate systems with only one B
particle so that BB interactions will not take place.

Is it possible to do it with Lammps, or the 'pair modify shift'
command will apply to all type of interactions? I would also

the shift part only applies to the energy.

to have a only repulsive potential, you simply need to set the
cutoff for that specific interaction at 2^(1/6) of the value of sigma.

cheers,
   axel.

The pair_modify shift and tail options apply to all pair styles
and type pairs. You can vary the cutoff for individual type
pairs via the pair_coeff command. As Axel said, the shift
part is just a bookkeeping term, it doesn't affect dynamics.
You can always add in a tail correction yourself if you want
some funky type-specific formula, and not the standard one.
Tail corrections assume a homogeneous system.

Steve

Shift terms can be important, however, if the density and/or density fluctuations in your system change. In those cases, usually you don’t want the system’s energy to change discontinuously when atoms come within range of each other. So, if you want to study something like (say) pressure-energy correlations, it’s usually considered wise to apply a shift even though it doesn’t affect the dynamics.

Best,
Rob