[gmx-users] REMD - step 12005: Water molecule starting at atom 7030 can not be settled
Mark Abraham
mark.j.abraham at gmail.com
Tue May 13 08:08:13 CEST 2014
On May 13, 2014 7:21 AM, "Steven Neumann" <s.neumann08 at gmail.com> wrote:
>
> Thanks a lot! So which combination of thermostat/barostat would provide a
> proper ensemble without crashes?
Various - but only P-R for the barostat in GROMACS, so you must be
conservative with REMD exchange period. That will depend on the system and
tau-p in a way that I expect nobody has studied. Hence avoiding NPT.
> I am looking in the literature but did not
> find anything.
Some discussion in the manual.
Mark
>
> On Tue, May 13, 2014 at 6:34 AM, Mark Abraham <mark.j.abraham at gmail.com
>wrote:
>
> > I would generally encourage the use of NVT REMD. However, note that P-R
> > does exhibit unstable oscillatory behaviour when not close to
equilibrium.
> > REMD is supposed to stay in equilibrium by design, but this gets double
> > crossed if the exchange period is too short with respect to the
> > autocorrelation of whatever is relevant, because a subsequent exchange
is
> > not from the right ensemble, so all bets are off.
> >
> > Mark
> > On May 13, 2014 4:01 AM, "Steven Neumann" <s.neumann08 at gmail.com> wrote:
> >
> > > Or just to switch to NVT? I guess it would be less realistic if one
wants
> > > to study extract the most likely conformation...
> > >
> > >
> > > On Tue, May 13, 2014 at 3:26 AM, Steven Neumann <s.neumann08 at gmail.com
> > > >wrote:
> > >
> > > > What would you recommend then? Equilibrate with Berendsen barostat
and
> > > > v-rescale thermostat?
> > > >
> > > >
> > > > On Mon, May 12, 2014 at 2:01 PM, Justin Lemkul <jalemkul at vt.edu>
> > wrote:
> > > >
> > > >>
> > > >>
> > > >> On 5/12/14, 3:58 AM, Steven Neumann wrote:
> > > >>
> > > >>> Dear Gmx Users,
> > > >>>
> > > >>> I am running REMD of a small protein in water. I have 36
> > temperatures.
> > > >>> After minimization I equilibrate each with nvt and npt ensemble.
> > Then I
> > > >>> start REMD with -multidir. The mdp:
> > > >>>
> > > >>>
> > > >>> ; Run parameters
> > > >>> integrator = md ; leap-frog integrator
> > > >>> nsteps = 50000000
> > > >>> dt = 0.002 ; 2 fs
> > > >>> ; Output control
> > > >>> nstxout = 0 ; save coordinates every 0.2 ps
> > > >>> nstvout = 0 ; save velocities every 0.2 ps
> > > >>> nstenergy = 5000 ; save energies every 0.2 ps
> > > >>> nstxtcout = 5000
> > > >>> nstlog = 5000
> > > >>> ; Bond parameters
> > > >>> continuation = no ; first dynamics run
> > > >>> constraint_algorithm = lincs ; holoyesmic constraints
> > > >>> constraints = all-bonds ; all bonds (even heavy atom-H
bonds)
> > > >>> constrained
> > > >>> lincs_iter = 1 ; accuracy of LINCS
> > > >>> lincs_order = 4 ; also related to accuracy
> > > >>> ; Neighborsearching
> > > >>> ns_type = grid ; search neighboring grid cells
> > > >>> nstlist = 5 ; 10 fs
> > > >>> vdwtype = Switch
> > > >>> rvdw-switch = 1.0
> > > >>> rlist = 1.4 ; short-range neighborlist cutoff (in nm)
> > > >>> rcoulomb = 1.4 ; short-range electrostatic cutoff (in nm)
> > > >>> rvdw = 1.2 ; short-range van der Waals cutoff (in nm)
> > > >>> ewald_rtol = 1e-5 ; relative strenght of the Ewald-shifted
> > > >>> potential
> > > >>> rcoulomb
> > > >>> ; Electrostatics
> > > >>> coulombtype = PME ; Particle Mesh Ewald for long-range
> > > >>> electrostatics
> > > >>> pme_order = 4 ; cubic interpolation
> > > >>> fourierspacing = 0.12 ; grid spacing for FFT
> > > >>> ; Temperature coupling is on
> > > >>> tcoupl = V-rescale ; modified Berendsen
> > > >>> thermostat
> > > >>> tc_grps = Protein Water_and_ions ; two coupling groups -
more
> > > >>> accurate
> > > >>> tau_t = 0.1 0.1 ; time constant, in ps
> > > >>> ref_t = 320.12 320.12 ; reference
> > > >>> temperature,
> > > >>> one for each group, in K
> > > >>> ; Pressure coupling is on
> > > >>> pcoupl = Parrinello-Rahman ; pressure coupling
is on
> > > for
> > > >>> NPT
> > > >>> pcoupltype = isotropic ; uniform scaling of
box
> > > >>> vectors
> > > >>> tau_p = 2.0 ; time constant, in ps
> > > >>> ref_p = 1.0 ; reference pressure,
in
> > > bar
> > > >>> compressibility = 4.5e-5 ; isothermal
> > > compressibility
> > > >>> of
> > > >>> water, bar^-1
> > > >>> refcoord_scaling = com
> > > >>> ; Periodic boundary conditions
> > > >>> pbc = xyz ; 3-D PBC
> > > >>> gen_temp = 320.12
> > > >>> DispCorr = EnerPres ; account for cut-off vdW scheme
> > > >>> gen_seed = 173529
> > > >>> gen_vel = yes ; assign velocities from Maxwell
distribution
> > > >>>
> > > >>>
> > > >>> I get the error: step 12005: Water molecule starting at atom 7030
can
> > > not
> > > >>> be settled. I tried to repeat it and I get the same error with
> > another
> > > >>> water molecule at different step. I am using Gmx 4.5.5
> > > >>>
> > > >>> I tried minimization many times lowering the maximum force by
> > steepest
> > > >>> descent, make the time step 1fs in equilibtration but it does not
> > > help. I
> > > >>> changed to force field as well and the same is happening. Please,
> > > advise.
> > > >>>
> > > >>>
> > > >> NPT REMD is often unstable because when switching the
configurations
> > > >> between conditions, the barostats can become unstable.
> > > >>
> > > >> -Justin
> > > >>
> > > >> --
> > > >> ==================================================
> > > >>
> > > >> Justin A. Lemkul, Ph.D.
> > > >> Ruth L. Kirschstein NRSA Postdoctoral Fellow
> > > >>
> > > >> Department of Pharmaceutical Sciences
> > > >> School of Pharmacy
> > > >> Health Sciences Facility II, Room 601
> > > >> University of Maryland, Baltimore
> > > >> 20 Penn St.
> > > >> Baltimore, MD 21201
> > > >>
> > > >> jalemkul at outerbanks.umaryland.edu | (410) 706-7441
> > > >> http://mackerell.umaryland.edu/~jalemkul
> > > >>
> > > >> ==================================================
> > > >> --
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