Using Tcl for molecular visualization and analysis

Reading and manipulating molecular structure data is a standard task in every molecular visualization and analysis program, but is rarely available in a form readily accessible to the user. Instead, the development of new methods for analysis, display, and interaction is often achieved by writing a new program, rather than building on pre-existing software. We present the Tcl-based script language used in our molecular modeling program, VMD, and show how it can access information about the molecular structure, perform analysis, and graphically display and animate the results. The commands are available to the user and make VMD a useful environment for studying biomolecules.