I've created a hybrid molecule to represent cholesterol tags on a scaffold. I connected 2 cholesterol atoms via user defined bonds between the ROH molecules of cholesterol. I've added a PO4 atom in between so the bond is ROH(Chol1) - PO4 - ROH(Chol2).
I would like to replace the PO4 molecule with a volume exclusion bead. How do I go about doing this? Is there any bead defined in martini that works as a volume exclusion bead, or would I need to write my own definition in Martini definitions itp.