Another strength of VMD lies in its ability to playback trajectories resulting from molecular dynamics simulations. A sample trajectory, alanin.DCD is provided in the proteins directory included with VMD. To load it, click on the Mol button of the button bar to bring up the Molecules form. Next click on the Load From Files button and select the psf and dcd option under the Molecule File Types listing. Select alanin.psf for the psf file and alanin.DCD for the DCD by clicking on the Select psf and Select dcd buttons respectively. After this, you need only click the Load Molecule button in order to begin reading the trajectory. In the display window you should see a simulation of an alanin residue in vacuo. It isn't particularly informative, but you can easily see that the structure is quite unstable in an isolated environment. After the DCD file has loaded, it will by default stop. To see it again or to fine- tune playback, open the Animate form by clicking on the appropriate button in the button bar. Press the button that looks like » to play the animation. Use the slider at the bottom of the form to change the speed of playback. By rotating the molecule around, etc. you should get an idea about how the system destabilizes over the course of the simulation.