# Gromacs Drude version **URL:** \ **Category:** User discussions\ **Created:** [March 3, 2021, 11:02am UTC](https://gromacs.bioexcel.eu/t/gromacs-drude-version/1673 "2021-03-03T11:02:56Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![bellafrizzo](https://avatars.discourse-cdn.com/v4/letter/b/b487fb/32.png) [@bellafrizzo](https://gromacs.bioexcel.eu/u/bellafrizzo)\ **Post date:** [March 3, 2021, 11:02am UTC](https://gromacs.bioexcel.eu/t/gromacs-drude-version/1673/1 "2021-03-03T11:02:56Z")
Hello there, I successfully simulated a ternary system water/solvent/phosphate with a low concentration of the latter. I just wanted to do the same with a increased amount of phosphate ions (let’s say 10 times). Minimization and nvt equilibrations are fine. NPT one gives a segmentation fault, namely step 28643: EM did not converge in 100 iterations, RMS force 10.914 step 28644: EM did not converge in 100 iterations, RMS force 130.329 step 28645: EM did not converge in 100 iterations, RMS force 435.571 step 28646: EM did not converge in 100 iterations, RMS force 834.122 step 28647: EM did not converge in 100 iterations, RMS force 1377.708 step 28648: EM did not converge in 100 iterations, RMS force 2349.287 step 28649: EM did not converge in 100 iterations, RMS force 4753.038 step 28692: EM did not converge in 100 iterations, RMS force 3.740 step 28693: EM did not converge in 100 iterations, RMS force 32.670 step 28694: EM did not converge in 100 iterations, RMS force 213.652 step 28695: EM did not converge in 100 iterations, RMS force 414.540 step 28696: EM did not converge in 100 iterations, RMS force 840.783 step 28697: EM did not converge in 100 iterations, RMS force 1445.265 step 28698: EM did not converge in 100 iterations, RMS force 2244.515 step 28699: EM did not converge in 100 iterations, RMS force 37.925 I post here the mdp. file I used: ; RUN CONTROL PARAMETERS ;define = -DPOSRES integrator = md ; Start time and timestep in ps tinit = 0 dt = 0.001 nsteps = 10000000 comm-mode = linear nstcomm = 100 comm-grps = System ; OUTPUT CONTROL OPTIONS nstxout = 1000 nstvout = 1000 nstfout = 1000 ; Output frequency for energies to log file and energy file nstlog = 100 nstcalcenergy = 1 nstenergy = 100 ; NEIGHBORSEARCHING PARAMETERS cutoff-scheme = verlet nstlist = 10 ns-type = Grid pbc = xyz rlist = 1.2 ; OPTIONS FOR ELECTROSTATICS AND VDW coulombtype = PME rcoulomb = 1.2 vdwtype = cutoff vdw-modifier = force-switch rvdw-switch = 1.0 rvdw = 1.2 DispCorr = EnerPres pme\_order = 4 fourierspacing = 0.1 ; TEMPERATURE COUPLING tcoupl = V-rescale ; Groups to couple separately tc-grps = System tau-t = 0.1 ref-t = 300 ; PRESSURE COUPLING IS NOT YET SUPPORTED pcoupl = Parrinello-Rahman pcoupltype = isotropic tau-p = 1.0 ref-p = 1.0 compressibility = 4.5e-5 refcoord-scaling = all ; GENERATE VELOCITIES FOR STARTUP RUN, OTHERWISE DO ; NOT GENERATE NEW VELOCITIES IF PREVIOUSLY EQUILIBRATED gen-vel = no gen-temp = 300 gen-seed = -1 ; OPTIONS FOR BONDS constraints = h-bonds ; can also be h-bonds, not all-bonds continuation = yes ; DRUDE PARAMETERS drude = yes drude-mode = SCF ;drude-rhyp = yes drude-khyp = 16736000.0 drude-r = 0.02 drude-pow = 4 emtol = 1.0 niter = 100 drude-hyper = yes Thank you in advance Matteo ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [March 4, 2021, 1:30pm UTC](https://gromacs.bioexcel.eu/t/gromacs-drude-version/1673/2 "2021-03-04T13:30:54Z")
Did you build, minimize, and successfully equilibrate with an additive force field first? Likely your initial conditions are simply too far from equilibrium to work. ---
**Author:** ![bellafrizzo](https://avatars.discourse-cdn.com/v4/letter/b/b487fb/32.png) [@bellafrizzo](https://gromacs.bioexcel.eu/u/bellafrizzo)\ **Post date:** [March 8, 2021, 9:28am UTC](https://gromacs.bioexcel.eu/t/gromacs-drude-version/1673/3 "2021-03-08T09:28:04Z")
Hi Justin, You mean equilibrate through the additive ff and then like pdb2gmx with the drude ff? ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [March 11, 2021, 3:37pm UTC](https://gromacs.bioexcel.eu/t/gromacs-drude-version/1673/4 "2021-03-11T15:37:38Z")
Yes, this is the conventional approach to preparing a polarizable system. It is easy to cause instability in an additive simulation, and **extraordinarily easy** to break a polarizable one, if any element of it is far from equilibrium.