[lammps-users] switching off the attractive part of the LJ potential

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1

Hi,

i’m interesting in studying a de-wetting problem. The liquid that de-wets and the substrate
that supports it interact via a LJ potential.

As an initial step in this simulation, one needs to create a liquid-film. To do so, it’s usual
to “sandwich” the film between two repulsive walls (i.e. walls that interact with the liquid
by means of the repulsive part of the LJ only). Subsequently, the attractive is switch on
and de-wetting starts. Also, by being able to control the attractive and repulsive part of
the LJ potential, one can see how changing the interactions changes the de-wetting.

To do the above, the LJ potential must look like this:

U=4epsilon(Crepulsive-D*attractive).

The LJ potential in lammps has a generic form, which in turn does not allow to switch
on-off the components of the LJ potential.

Is this so? And if so, is there a way one can use within lammps to switch off the attractive
part of the LJ potential?

Thanks
Miguel

2

Hi,

[...]

To do the above, the LJ potential must look like this:

U=4*epsilon(C*repulsive-D*attractive).

The LJ potential in lammps has a generic form, which in turn does not allow
to switch
on-off the components of the LJ potential.

Is this so? And if so, is there a way one can use within lammps to switch
off the attractive
part of the LJ potential?

miguel,

all you have to do is to shift the potential so that the minimum
is a zero energy and then set the cutoff to that radius.

the cg/cmm angle potential (part of the CG-CMM user package)
uses the repulsive part of a lennard-jones type potential only.
the math is straightforward. :wink:

cheers,
   axel.

3

douh! that sounds like reasonable :slight_smile:

Thanks
Miguel