SurfaceAnchorage

The SurfaceAnchorage potential models the interaction between particles and a planar surface using a harmonic well within a certain range. It is useful for simulating tethered or anchored particles on a surface.

\[\begin{split}U(z) = \begin{cases} \frac{1}{2}\epsilon\left(\frac{z - z_s}{\sigma}\right)^2 - \frac{1}{2}\epsilon, & \text{if } |z - z_s| \leq \sigma \\ 0, & \text{otherwise} \end{cases}\end{split}\]

where:

  • \(\epsilon\) is the well depth

  • \(\sigma\) is the width of the well

  • \(z\) is the z-coordinate of the particle

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

  • type: Surface, SurfaceAnchorage

  • parameters:

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

  • data:

    • name: string: Name of the particle type

    • epsilon: real: Well depth \(\epsilon\) \([energy]\)

    • sigma: real: Width of the well \(\sigma\) \([distance]\)

Example:

"surfaceAnchorage":{
  "type":["Surface","SurfaceAnchorage"],
  "parameters":{
    "surfacePosition": 0.0
  },
  "labels":["name", "epsilon", "sigma"],
  "data":[
    ["A", 10.0, 1.0],
    ["B", 5.0, 1.5]
  ]
}

Note

The force is only applied in the z-direction, perpendicular to the surface, and only within the range \(|z - z_s| \leq \sigma\). Outside this range, both the energy and force are zero.

Tip

SurfaceAnchorage can be used to model particles tethered to a surface with some flexibility or to create a soft wall boundary condition with a finite range of interaction.