Lattice Waves in a Three-Dimensional KBr Crystal

This animation shows lattice waves in a three-dimensional crystal of KBr.

The red spheres are potassium ions (K+), and the yellow spheres are bromine ions (Br-). The animation starts with a longitudinal wave in the acoustic branch (LA) with a wavelength equal to the lattice parameter a. The wave is traveling in the +x direction, as indicated by the k vector.

The program recognizes the following commands. The command may be executed by either clicking the button with the mouse (first column below) or by pressing a key (second column below). The mouse buttons may be removed from the screen by pressing the M key. Press M again to restore buttons.

xx Polarization of wave in x direction (longitudinal wave)
yy Polarization of wave in y direction (transverse wave)
yy Polarization of wave in z direction (transverse wave)
To change to waves in the optical branch, click on the "acoustic branch" button (or press the "o" key). The label on the button will change to "optical branch." To change waves back to the acoustic branch, click on the button again (or press the "a" key).

To change the wavelength, simply enter at the keyboard any positive number (may include decimal point). Press the "enter" key at the end of the number. This number is the wavelength as a multiple number of lattice constants a.