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