By default, the set of parameters used in PARAM is that stored inside the program. However, during method development and testing it is often desirable to use parameters supplied from files. This is like the MOPAC keyword EXTERNAL=<text> When PARAMS=text[;text[;text[;text]]] is present, the default set of parameters is overwritten by the entries in files defined by the keyword.
Example: params=..\PM7\params.txt;br.rp
In this example, the entries in params.txt would be read, and the appropriate parameters in PARAM updated, then the entries in br.rp would be read and the appropriate parameters in PARAM again updated.