ESP constrain options

Just Got Here
I would like to set a constrain option during esp fitting to avoid negatively charged atoms. I understand that this is not a standard command, but I found in another thread the suggestion to modify the esp_input.F file to include this option for myself.
1. Where is the esp_input.F file located? I installed nwchem through a .deb file and I am unsure of where the working files are.
2. I am looking at an esp_input.F file of an older computer and I cannot tell what computing language it is written in. Any thoughts?

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