Optimize With Distance Constraint

I have have a system consisting of two molecules and Cl- anion. I want to optimize the whole system but maintain the distance (freeze the distance) between the Cl- and the proximal proton on the one molecule.

How can I do this?


In order to freeze the distance between atoms 1 and 2 use

set optking {
frozen_distance = ("
1 2

Good luck, have fun!

thanks for the help!