SurfaceWCA

The SurfaceWCA potential models the interaction between particles and a planar surface using the Weeks-Chandler-Andersen (WCA) potential. It is a purely repulsive potential, useful for modeling excluded volume effects near surfaces.

There are two types of SurfaceWCA potentials implemented:

SurfaceWCAType1

\[\begin{split}U(z) = \begin{cases} 4\epsilon \left[ \left(\frac{\sigma}{z-z_s}\right)^{12} - \left(\frac{\sigma}{z-z_s}\right)^6 \right] + \epsilon & \text{if } z-z_s < 2^{1/6}\sigma \\ 0 & \text{if } z-z_s \geq 2^{1/6}\sigma \end{cases}\end{split}\]

SurfaceWCAType2

\[\begin{split}U(z) = \begin{cases} \epsilon \left[ \left(\frac{\sigma}{z-z_s}\right)^{12} - 2\left(\frac{\sigma}{z-z_s}\right)^6 \right] + \epsilon & \text{if } z-z_s < \sigma \\ 0 & \text{if } z-z_s \geq \sigma \end{cases}\end{split}\]

where:

  • \(\epsilon\) is the energy scale of the interaction

  • \(\sigma\) is the characteristic distance

  • \(z\) is the distance of the particle from the surface

  • \(z_s\) is the position of the surface

  • type: Surface, SurfaceWCAType1 or SurfaceWCAType2

  • parameters:

    • surfacePosition: real: Position of the surface along the z-axis \([distance]\)

  • data:

    • name: string: Name of the particle type

    • epsilon: real: Energy scale of the interaction \([energy]\)

    • sigma: real: Characteristic distance \([distance]\)

Example:

"surfaceWCA":{
  "type":["Surface","SurfaceWCAType1"],
  "parameters":{
    "surfacePosition": 0.0
  },
  "labels":["name", "epsilon", "sigma"],
  "data":[
    ["A", 1.0, 1.0],
    ["B", 0.5, 0.8]
  ]
}

Tip

This potential is particularly useful for simulating non-adsorbing surfaces or creating effective walls in simulations.