Thank you for your great help on specbond.dat file. I defined it and I could go ahead until Energy minimization step. I have used this minim.mdp file
; minim.mdp - used as input into grompp to generate em.tpr ; Parameters describing what to do, when to stop and what to save integrator = steep ; Algorithm (steep = steepest descent minimization) emtol = 1000.0 ; Stop minimization when the maximum force < 1000.0 kJ/mol/nm emstep = 0.01 ; Energy step size nsteps = 50000 ; Maximum number of (minimization) steps to perform ; Parameters describing how to find the neighbors of each atom and how to calculate the interactions nstlist = 1 ; Frequency to update the neighbor list and long range forces ns_type = grid ; Method to determine neighbor list (simple, grid) rlist = 1.0 ; Cut-off for making neighbor list (short range forces) coulombtype = PME ; Treatment of long range electrostatic interactions rcoulomb = 1.0 ; Short-range electrostatic cut-off rvdw = 1.0 ; Short-range Van der Waals cut-off pbc = xyz ; Periodic Boundary Conditions (yes/no) But when I run mdrun -v -deffnm em command, I get this error: Energy minimization has stopped, but the forces have not converged to the requested precision Fmax < 1000 (which may not be possible for your system). It stopped because the algorithm tried to make a new step whose size was too small, or there was no change in the energy since last step. Either way, we regard the minimization as converged to within the available machine precision, given your starting configuration and EM parameters. Double precision normally gives you higher accuracy, but this is often not needed for preparing to run molecular dynamics. You might need to increase your constraint accuracy, or turn off constraints altogether (set constraints = none in mdp file) writing lowest energy coordinates. Steepest Descents converged to machine precision in 90 steps, but did not reach the requested Fmax < 1000. Potential Energy = -2.3956744e+05 Maximum force = 1.5824519e+05 on atom 380 Norm of force = 1.7695243e+03 gcq#187: "Been There, Done It" (Beavis and Butthead) farideh@farideh-P61A-D3:~/FARIDEH$ I changed the emtol, emstep, and nsteps for a few times. However, I couldn't resolve this problem. Could you tell me if there is something wrong with the minim.mdp file? You can see all the files via: https://www.dropbox.com/s/sq2c103yxi4mc28/Farideh.zip?dl=0 Truly yours, Farideh -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org.