Seeing the Physics of Chemistry

Abstract

S tark Design's 3-D Molecular Dynamics (3DMD) program uses state-of-the-art interactive visualization software to simulate atomic motion. Although the target audience is the typical college undergraduate student, the software is also useful for advanced physical chemistry and graduate students. The four main modules of the program are Introductory Topics, Gas Behavior, Condensed Phases, and Advanced Topics, which covers most of the basic chemical principles. These include Dalton's law of partial pressure, diffusion, Maxwell-Boltzmann speed distribution, pressure/temperature and pressure/volume relationships, LeChatelier's principle, collision frequency, mean free path, pressure fluctuations, and the time average of kinetic energy. To view one of the concepts, a student picks a module and specific experiment from the home screen. For example, to study diffusion, the Gas Behavior module is chosen and diffusion is selected from the list of choices. A box appears that is divided into two compartments by a barrier (see figure). The opening between the chambers can be resized as desired. Next, the user selects atoms (helium, krypton, argon, and neon are the only choices) and introduces a specified number of each type into the system. The size of each atom is a function of its Van der Waals radius. By adjusting the temperature and time periods per screen update (with sliding switches), the atomic motion may be increased or slowed. This allows one to view the effect each parameter has on ultimately reaching equilibrium across the opening. In the Condensed Phases module, molecules actually “form” and “degrade” as the temperature changes. These processes may be hastened, or retarded, by the inclusion or exclusion of user-specified interatomic forces. While all this is happening, users can switch between two views—atoms as spheres or the classical view of atoms as circles with attached vectors. In addition to the molecular animations, two graphs are also visible for the diffusion module. The topmost graph displays the average position of an ensemble of atoms in the box in real time, and the bottom graph describes the relation between the atomic velocity and the square root of the ratio of the mass of a helium atom to the mass of any of the other three. The clever use of visualizations, combined with relevant graph plots, is a feature of all of the modules. Unfortunately, in the present version only Macintosh users can print screen views. A short, clearly written manual describing each module accompanies the CD-ROM. The manual is largely free of mathematics, except as necessary to support the program's atomic illustration functions. 3-D Molecular Dynamics succeeds in teaching basic physical-chemical principles with clever visualizations. The addition of other atoms and even small molecules would be a welcome addition to future editions. The program comes in both Macintosh and Windows formats. 3-D Molecular Dynamics version 2.5 Stark Design, Inc. Morristown, NJ. $180 877-384-8021