Interfacial tension:Basic Layout

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Etomica Modules

When the Interfacial Tension module is started it looks like this:

IT pic3.gif

At the bottom of the display is the control panel, which contains controls that allow the user to interact with the simulation. It contains buttons that:

  1. Start and stop the simulation (Start button)
  2. Restart the simulation from its initial state (Reinitialize button)
  3. Reset averages by discarding any previous contributions (Reset averages button)
  4. Expand the box to allow the formation of the vapor phase (Expand button)

Once the system has equilibrated for a short period of time, the cubic simulation box can be immediately expanded in the "x" direction by pressing the Expand button. When pressed, the "x" dimension of the simulation box is expanded by a factor of 3, which subsequently allows some of the liquid-phase molecules to evaporate to the newly-created vapor phase. Once this new two-phase simulation has been allowed to equilibrate, a representative simulation snapshot may look like:

IT pic4.gif

On the left side of the display is a section that contains simulation start–up settings (listed under three different tabs) that can be adjusted by using sliders or by typing in a numerical value. Under each tab, the following adjustments can be made:

  • System: the box size and the temperature can be adjusted.
  • Surfactant potential: the values of the surfacant head (epsilon) and tail (sigma) can be adjusted.
  • # of molecules: the number of atoms in the box can be varied (default=643), and the number of surfactant molecules can be varied (default=0). It is important to note that the the surfactant molecules are added to the system after the Expand button is pressed. Furthermore, the number of surfactant molecules cannot be adjusted after the Expand button has been pressed. Once the box has been expanded, the number of sufactant molecules are "locked-in".

    The center section of the display is referred to as the “Graphics Panel”. The Graphics Panel contains a visualization of the simulation and dynamically-updated data plots, displayed under a series of tabbed pages. Under the Configuration tab, the current configuration of the system can be visualized. Using the mouse, the scene can be rotated (left-mouse-button) or translated (right-mouse-button) within the visualization screen. Under the tabs Virial Profile, Tension Profile, Density, and Chemical Potential, the respective quantities are reported as a function of the x-dimension of the simulation box. In this way, the values of each of these quantities can be analyzed and compared within the vapor phase, liquid phase, and at the vapor-liquid interface. The Orientation tab represents the orientation of the surfactant molecules (also as a function of the x-dimension), so this graph is only useful for simulations that have surfactant molecules present. The Energy tab charts the potential energy history of the system as a function of time. Finally, under the Metrics tab, numerical values of some of the main results of the simulation are reported, which are updated continuously while the simulation is running: the Virial contribution in the x, y, and z dimensions, the Potential Energy of the system, and the Interfacial tension. The Current value (value calculated for each time block), running Average, and statistical Error are listed for for each.