F. Tim Janis and Eugene J. Peterson1 Illinois Benedictine College Lisle, 60532
UNIQUE-An Interactive Quantum Mechanical Program
With the widespread availability of real time computer systems it is now possible to conceive of novel types of chemistry experiments. This becomes especially useful in the area of atomic and molecular structure determination when the methods of quantum mechanics are employed. Most of the models used are abstract mathematical models and therefore cannot he observed within the normal laboratory framework. A computer can be programmed to simulate (evaluate) the model and thereby becomes an "instrument'' that will measure (produce) the properties that the model predicts. By designing an appropriate sequence of questions to which the "instrument" can respond, the user may "experiment" with the model. A careful grouping of these questions produces a new type of experiment. UNIQUE (Undergraduate Interactive Quantum-chemical Experimental-system) was conceived to implement this idea. A number of computing systems capable of doing chemistry exist;2 however, only a few, such as BISON3 and MOLE,' are encompassing enough to be able to answer a variety of questions. These systems are not interactive and are research tools not intended for use in an undergraduate program. The model we chose for study and implementation was the simple Huckel method.= The system was designed to contain the following modules: descriptive, instructional, and computational. The descriptive module was written in Basic and provides the user with instructions on how to use the system. It lists the names, calling sequence, etc. for the working modules. The instructional module was designed to provide theoretical information about the Huckel method. I t is a tutorial section, coded in Basic, describing the method. I t has multiple entry points and allows various levels of questions ranging from basic definitions to a complete description of the secular equation. We felt two types of computational modules were necessary: one that allowed for real time computation of properties and one that searched a library of precalculated wave functions. This would allow UNIQUE to be used on either a large or small computer system. Because of the limitation of our own computing system we chose to implement the latter method first. A "standard" batch mode Fortran version of the Huckel method was written and calculations were done on benzene and benzene derivatives a t various geometries with
622 /Journal of Chemical Education
different parameters. The energies and wave functions were tabulated and stored. The computational module was then produced from a set of programs coded in Basic. These programs retrieve the wave functions and generate upon request the charge densities, electron densities, bond orders, dipole moments, free valences, total energies, resonance energies, and excitation energies. Each quantity may be requested separately or all may be ohtained collectivelv. -...---" The modules were designed so that the following types of questions could be asked and answered interactively. 1) What happens to the stability of a n-electron system as the bondlengthens or as bond angles are changed? 2) Determine the most stable geometry for a system. 3) How does the charge density change as suhstituents are added? 4) Show where and what types of groups might attack the system. 5) Determine where the model breaks down. 6) How significant is the choice of parameters? ~
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Appropriate combinations of these questions and others like them yield an excellent advanced physical chemistry experiment. Conclusion
The advantaee of UNIQUE is that it allows the student to thoroughly investigate- the model and reach his own conclusion as to its viability and ~redictability. The Huckel program, -the &structional module, and portions of the computational module are available upon request. The experiment is still in the preliminary stages of development and will be made available a t a later date. 'Submitted a s a thesis in partial fullfillment for degree of Bachelor of Science in chemistrv at Illinois Benedictine College. Presently at Arizona State university. ZSee for example "Quantum Chemistry Program Exchange Catalog," Indiana University. 3 Wahl, A. C., Bertoncini, P. J., Kaiser, K., and Land, R. H., "BISON-A FORTRAN Computing System far the Calculation of Wavefunctions, Properties, and Charge Densities for Diatomic Molecules," ANLRepart No. 7271, 1968. 'Rattenberg, S., Collman, P., Sehwartz, M. E., Hayes, E. F., and Allen, L., "System for Quantum Chemistry IJQC," 35, 715 (1910).
Huckel, E., Z. Physik 70,204(1931).
