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> but is more flexible. When EXTERNAL=text[;text[;text[;text]]] is present, the default set of parameters is overwritten by the entries in files defined by the keyword. Each file can be defined by quotation marks; these are only necessary if there are spaces in the file name or in its path.
Example:
EXTERNAL=..\PM7\params.txt;&
br.rp; &
"test data set.rp"
In this example, the entries in "params.txt" would be read, and the appropriate parameters in PARAM updated, followed by the entries in "br.rp" and, finally the entries in "test data set.rp".