Ziman explores the dynamics of a single electron in a band. In this preset there are no applied fields. The constant energy contours are displayed on the right and the red dot is an initial position of the electron in k-space. In real space on the left the electron is always started at the origin. Click on run to see the motion.
In absence of applied fields, the electron remains at a fixed point in k space. It moves in real space with the group velocity appropriate to that point in k-space. Clicking with the left mouse button on a point in k-space reinitializes the program with the initial k at the position of the cursor. (There is no need to stop the program--you can reinitialize "on the fly".) Try clicking on a variety of points in k-space and be sure that you can predict the direction (and magnitude) of the velocity in real space.
Try clicking on a point on (or at the center of) one of the edges of the Brillouin zone.