Dear all, Maybe is a easy question but I'm really confused. Genpair is only for the 1-4 interactions or for all vanderwalls interacions not defined. I'm using Gromcacs force field in convination with lipid.itp. And in the defaults genpairs is set to no( ffgmx.itp) that is the correct one or its easier to set it to yes. Thanks in advance Hector