PARAM is a program for optimizing parameters for semiempirical methods. It is controlled by a single data set that specifies the type of operation (usually parameter optimization or a survey to determine errors), the conditions for the operation (AM1, PM6, etc., or a new method), and the set of data-files to be used.
In the past, parameter optimization was very difficult. Finding the minimum in parameter space was a major undertaking. These problems have now been solved; the main problem now is specifying what is to be optimized, and determining if the result of an optimization is an improvement over existing methods.
The program PARAM is the central program used for method development. There are several utility programs (see PROGRAMS) that are useful in manipulating the large files and large number of files. Before using the program PARAM, first become familiar with these utilities.
PARAM uses several types of files. For convenience, these should be stored in different folders, so each folder contains only one type of file. The main types are normal data sets, data sets representing atomic states, data sets for exotic systems, data sets for PARAM, and data sets for parameters. This last set does not need to exist - if it does not exist, PARAM will use parameters from the default method.
If, as is inevitable, things go wrong, there are extensive diagnostics available for finding out what happened. These diagnostics can also indicate what to do, but of course they cannot take any action on their own. Options also exist to identify faulty data, and, depending on the keywords used, either ignore, i.e., exclude, the faulty data or stop the calculation, so the user can take appropriate action.