Dear Gromacs Users, I am trying to add the tetrahedral zinc atom dummy model into CHARMM36 force field in Gromacs. In my system, this dummy zinc interact with four Cystein residues (CYM). The parameters of the zinc are available in CHARMM format, which I used to use it in NAMD package. After adding appropriate parameters, when I do energy minimization, 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). ... Steepest Descents converged to machine precision in 1045 steps, but did not reach the requested Fmax < 1000. Potential Energy = -1.5922652e+06 Maximum force = 3.2106902e+07 on atom 3526 Norm of force = 1.4857810e+05 ============================ Atom 3526 is dummy atom of zinc ion. The dummy parameters added in ffbonded.itp file are: ---------- ffbonded.itp ;zinc dummy model, bonds HK ZD 1 0.09000000 451872.00 HK HK 1 0.14700000 451872.00 ;zinc dummy model, angles HK ZD HK 5 109.500000 460.240000 0.00000000 0.00 HK HK HK 5 60.000000 460.240000 0.00000000 0.00 HK HK ZD 5 35.250000 460.240000 0.00000000 0.00 ;zinc dummy model, dihedrals ZD HK HK HK 9 35.300000 0.000000 2 HK ZD HK HK 9 120.000000 0.000000 2 HK HK HK HK 9 70.000000 0.000000 2 ----------- ffnonbonded.itp ;zinc dummy model ZD 30 61.380000 0.000 A 0.310000000000 0.00001 HK 1 1.008000 0.500 A 0.000000000000 0.00000 ================================================= In contrast to Gromacs, when I do minimization in NAMD, there is no such an error in minimization. I should mention that I am using single precision platform of Gromacs. I would appreciate if you could share me in case you have some ideas about this problem. Cheers, Mahdi -- 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.