This is for out newly developed water model OPC3-B. The parameter files in the current directory should be moved to your Amber software installation path.
To be more precisely, the file leaprc.water.opc3b should be placed in the path of $PATH_TO_AMBERHOME/dat/leap/cmd, and the frcmod.opc3b should be placed in $PATH_TO_AMBERHOME/dat/leap/parm
Then you can use source leaprc.water.opc3b to load OPC3-B in your tleap commands.
And use the command of OPC3BOX to load the OPC3-B water box.