Kenneth 0. Wiberg Yale University N e w Hoven, Connecticut 06520
The Small Computer in the Laboratory
For many years, computers have normally been large general purpose instruments designed to handle the needs of a major body of users. However, in recent years, a group of small computers have become available in the $8000-20,000 price range. Even the least expensive of these has a memory which can store 4096 twelve bit words. Each word corresponds to one instruction or one datum. I n addition, they have a teletype with paper tape punching and reading facilities for input to and output from the computer, a moderately large group of instructions, and the possibility of adding a variety of external devices which may be operated by the computer. These computers have great potential in both undergraduate instruction and in graduate research in chemistry. The following will indicate some of the more useful applications. It is generally agreed that some experience with computers is desirable for undergraduates. Three approaches are possible. A large computer may be used in a "batch" mode in which the student prepares his program on cards, leaves them with the computer operator, and returns latcr to obtain his results. Second, a large computer may be used in an "interactive" mode. Here, many teletypes are attached to the computer, and each person types his program using the teletype. The amount of act,ual interaction varies -some systems check each statement as it is typed and immediately supply error messages whereas others check for errors only after the entire program has been typed. The third approach is to use a small computer, again operating from the teletype. The first approach is usually the least efficient for undergraduate students since errors can be corrected only by changing cards and resubmitting the programa time consuming process. The second two approaches are, for short programs, essentially equivalent. However, for smaller schools a large computer may be too expensive to he supported, whereas one or more of the small computers might be within reason. Also, it is relatively expensive to provide television type output facilities (for data plotting, rapid output, etc.) with a large computer, whereas it is relatively inexpensive with a small computer. As will be indicated later, a computer is very useful for data collection and control. I n many cases, it is still difficult to collect data directly from an instrument using a time shared large computer. The small computers can do this easily. Thus, in many cases, the small computers have real advantages over the larger instruments. A final consideration is that This work was supported by a grant from the National Science Foundation.
students have much more of an opportunity to learn about computers when using a small computer themselves than when tied in to a large computer. What are the advantages in using computers in undergraduate chemistry courses? I n the general chemistry, analytical chemistry, and physical chemistry courses, a major component of the instructional process is solving problems. These have generally been of a relatively simple type which could easily be solved using a slide rule because more complex and valuable problems have required an impractical amount of the students' time. The small computers may be used in a "desk calculator" mode in which one types the equation to be evaluated, and the computer performs the evaluation including the calculation of trignometric, exponential, and logarithmic functions. This will suffice to handle a wide variety of problems and ensures that the arithmetic will be done correctly. For more complex problems, programs may easily be written using BASIC, FOCAL, or similar languages which are learned with no more than a few hours instruction. Since the numerical answers are obtained, the students have a better opportunity to check whether or not their method of setting up the problem is correct. A more important task is that of data reduction, as in fitting a set of experimental data to an analytical expression by a method such as that of least squares. Here, the student has a possibility of treating his data in a really careful fashion and to critically examine the errors in his data and in the derived quantities. The relatively long and tedious calculations which are required for such calculations normally discourage both the instructor and the student from carrying them out. The student now has an opportunity to make a careful analysis of the data he obtains in laboratory experiments, particularly in the physical chemistry laboratory. The main restriction in the use of small computers is that the amount of data storage must be kept to a minimum because of the small memory. If the problem involves only a relatively small amount of data, the program may be written in Fortran, or in the simpler Fortran like languages such as BASIC and FOCAL. Here, the arithmetic operations may be written in essentially the normal algebraic form, and the computer, with the aid of a program known as a compiler, will work out the sequence of individual steps needed to evaluate the algebraic expressions. These languages are easily learned and after a few hours of study st,udents are able to write simple computer programs. Common calculations of the type referred to above include the calculations of rate constants, of activation parameters, of dipole moments, and of nmr spectra (for simple cases). These calculations are often needed in Volume 47, Number 2, February 1970
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