[gmx-users] How to select atoms between 2 molecules and then calculate rdf

[1185201182]

Dear Gromacs users
I have finished a simulation. I have two molecules with different resnames, e.g res1, and res2, there are water atoms between them, meanwhile the distance of center of mass between two molecules are changing during simulation. So I wonder how can I calculate the rdf of water which is enclosed by the plane cross the center of res1 and the res2, for example rdf between Oxygen and Oxygen?
I checked the gmx_select, but I still do not know how to do it.

Could any body give me a little help about it?

Thanks.

Fan