Exercises

In NetLogo model 6.8.1, we have a model that shows a close-packed crystal structure in 2D. In this model, the bonds are shown in light gray lines and the atoms are represented by circles. We're able to observe two things is this model: the state of the bond (in compression, tension, or equilibrium) and the potential energy of the atom.

In Exercise 6.8.1, let's explore the model to see what happens when we start to introduce point defects into the structure.

Exercise 6.8.1: Exploring Defects
Not Currently Assigned

  1. Use the default settings on the model in NetLogo model 6.8.1. Press setup and go.

    What do you observe about the state of the bonds and the potential energy of the atoms? Note, we want the assembly to stay in place, so we've fixed the bottom row of atoms.

  2. Now, change click mode to delete-atom.

    1. Delete the blue atom in the "center" of the structure. What happens?
    2. Press setup again. Now try deleting a different atom and running the model again. Do this until you observe something new. What do you observe, and why?

  3. Press setup to reset the model and change click-mode to add-atoms. Place an atom in a triangular interstitial site. You have to be pretty precise with the placement! Putting it too close to another atom will make the system explode.

    1. What do you observe about the effect of the addition of the small atom?
    2. Now change click-mode to select-atom. Select the interstitial atom you just created. You should see a small "S" appear on the atom. Increase the size of the atom such that it is about the same size as the atoms in the host lattice. What do you observe?
    3. In what conditions do you think a structure could tolerate a large atom in an interstitial site without inducing reorganization?
Exercise 6.8.2: Hume-Rothery Application
Not Currently Assigned

  1. Order the elements (Sr, Al, Ag, Co) in Figure 6.8.1 from highest to lowest solubility in Zn (top row).

Some elements and the pertinent data for applying the Hume-Rothery rules.

Figure 6.8.1 Some elements and the pertinent data for applying the Hume-Rothery rules.