Dear Gromacs pals: I need to add a 30-6 LJ potential to deal with a defect in Buckingham, that is U goes to -inf when r -> 0. 30-6 LJ has the following form: U(r)=4epsilon( (sigma/r)^30 - (sigma/r)^6 ) Do you know to build up this potential in Gromacs? Thank you very much! Lianqing