I am trying to use the pull code integrated in Gromacs to perform a test QM/MM calculation consisting of H30+ and H20. I am trying to transfer a hydrogen from the H30+ to H20. What are the parameters (if any) that I should be using besides the common ones such as the one from http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin/gmx-tutorials/umbrella/05_pull.html :

; Pull code pull = yes pull_ngroups = 2 pull_ncoords = 1 pull_group1_name = pull_group2_name = pull_coord1_type = umbrella ; harmonic biasing force pull_coord1_geometry = distance ; simple distance increase pull_coord1_groups = 1 2 pull_coord1_dim = N N Y pull_coord1_rate = 0.01 ; 0.01 nm per ps = 10 nm per ns pull_coord1_k = 1000 ; kJ mol^-1 nm^-2 pull_coord1_start = yes ; define initial COM distance > 0

Thank you.