[gmx-users] issue in replica exchange
Simone Conti
simonecnt at gmail.com
Thu May 2 12:38:35 CEST 2013
I'm running remd in NPT ensemble for a small peptide and all is ok if the
maximum temperature is below 510/520 kelvin. I use Nosé-Hoover termostat
and Parrinello-Rahman barostat. Ref T from 285 to 500K and ref P equals to
1bar. Gromacs version 4.5.5. Exchange trials every 5 ps.
If I try to add replica at a higher temperature the system crash, but I
think it is a problem of equilibration.
2013/5/1 XAvier Periole <x.periole at rug.nl>
>
> Ok here is my current status on that REMD issue.
>
> For info: I use
> Temperature: v-rescale, tau_t = 2.0 ps
> Pressure: berendsen, tau_p = 5.0 ps,
> time step: dt=0.002 - 0.020 fs,
> COM removal on for bilayer/water separately
>
> The symptoms: explosion of the system after 2-5 steps following the swap,
> first sign is a huge jump in LJ interactions and pressure. This jump seems
> to be absorbed by the box size and temperature when possible … see example
> I provided earlier. A large VCM (velocity centre of mass?) is often
> associated with the crash. But also pressure scaling more than 1% ...
>
> 1- the problem mentioned above remains in gmx-4.5.7 and it might actually
> got worse. I was able to run a 500 ns simulation with gmx405 using similar
> setup as for gmx457. The following point happened in gmx457.
> 2- it persists with a time step of 2 fs. Actually all tests performed in
> the following used dt=2fs.
> 3- if I perform an exchange that explodes within mdrun myself (externally
> to the remd gromacs by getting the gro file with the mdp adjusting the
> temperature) it goes all fine.
> 4- the issue gets much worst when the consecutive replicas differ
> (different protein conformations and the box size etc) … explosion at first
> exchange.
> 5- the use of parrinelo-raman does not help
> 6- cancelling the centre of mass removal does not remove the problem.
> 7- switching to NVT ensemble does not help but makes it worst (crash in 2
> steps). All exchanges accepted at first attempt crash with the message
> "Large VCM(group SOL): -0.0XXX , -0.XXX, -0.16XXX, Temp-cm:6.55XXX
> 8- using a unique conformation (the same) for all replicas in the NVT REMD
> simulation after equilibration in the same NVT ensemble (for 1 ns) removes
> the problem.
> 9- taking the equilibrated NVT conformations, equilibrate them in an NPT
> ensemble (1 ns) and let go the exchanges afterwards restores the problem …
> one exchange is not properly done at the second trial, while the first ones
> were fine. Well if errors were made that was with reasonable
> 10- note also that the coarse grain I use is extremely forgiving, meaning
> you can perform really nasty transformations and run it further after
> simple minimisation … so even abrupt changes in temperatures should be fine
> and relax quickly.
> 11- when looking at the conformations themselves nothing appears to have
> jumped over or nothing funky.
>
> At this point I am not sure what to think and what to do next. There is
> definitely something not going right during the exchanges.
>
> Anyone has been able to run a REMD simulation in an NPT ensemble without
> crashes? I would imagine someone has and something particular to my system
> is making it going wrong but I am really wondering what it could be. My
> feeling is that something relative to the box size or pressure is not going
> across but it might be something completely different, when the consecutive
> systems differ reasonably.
>
> However that would suggest that the manner the exchanges are made is
> severely wrong in some cases.
>
> Any help to resolve the problem would be greatly appreciated.
>
> XAvier.
>
> On Apr 26, 2013, at 9:21 AM, Mark Abraham <mark.j.abraham at gmail.com>
> wrote:
>
> > On Thu, Apr 25, 2013 at 11:05 PM, XAvier Periole <x.periole at rug.nl>
> wrote:
> >
> >>
> >> Thanks for the answer. I'll check gmx4.5.7 and report back.
> >>
> >> I am not sure what you mean by GROMACS swaps the coordinates not the
> >> ensemble data. The coupling to P and T and not exchanged with it?
> >
> >
> > The code in src/kernel/repl_ex.c:
> >
> > static void exchange_state(const gmx_multisim_t *ms, int b, t_state
> *state)
> > {
> > /* When t_state changes, this code should be updated. */
> > int ngtc, nnhpres;
> > ngtc = state->ngtc * state->nhchainlength;
> > nnhpres = state->nnhpres* state->nhchainlength;
> > exchange_rvecs(ms, b, state->box, DIM);
> > exchange_rvecs(ms, b, state->box_rel, DIM);
> > exchange_rvecs(ms, b, state->boxv, DIM);
> > exchange_reals(ms, b, &(state->veta), 1);
> > exchange_reals(ms, b, &(state->vol0), 1);
> > exchange_rvecs(ms, b, state->svir_prev, DIM);
> > exchange_rvecs(ms, b, state->fvir_prev, DIM);
> > exchange_rvecs(ms, b, state->pres_prev, DIM);
> > exchange_doubles(ms, b, state->nosehoover_xi, ngtc);
> > exchange_doubles(ms, b, state->nosehoover_vxi, ngtc);
> > exchange_doubles(ms, b, state->nhpres_xi, nnhpres);
> > exchange_doubles(ms, b, state->nhpres_vxi, nnhpres);
> > exchange_doubles(ms, b, state->therm_integral, state->ngtc);
> > exchange_rvecs(ms, b, state->x, state->natoms);
> > exchange_rvecs(ms, b, state->v, state->natoms);
> > exchange_rvecs(ms, b, state->sd_X, state->natoms);
> > }
> >
> > I mis-stated last night - there *is* exchange of ensemble data, but it is
> > incomplete. In particular, state->ekinstate is not exchanged. Probably it
> > is incomplete because the 9-year-old comment about t_state changing is
> in a
> > location that nobody changing t_state will see. And serializing a
> complex C
> > data structure over MPI is tedious at best. But that is not really an
> > excuse for the non-modularity GROMACS has for many of its key data
> > structures. We are working on various workflow and actual code structure
> > improvements to fix/prevent issues like this, but the proliferation of
> > algorithms that ought to be inter-operable makes the job pretty hard.
> >
> > Other codes seem to exchange the ensemble label data (e.g. reference
> > temperatures for T-coupling) because they write trajectories that are
> > continuous with respect to atomic coordinates. I plan to move REMD in
> > GROMACS to this approach, because it scales better, but it will not
> happen
> > any time soon.
> >
> > That would explain what I see, but let see what 4.5.7 has to say first.
> >>
> >
> > Great. It may be that there were other issues in 4.5.3 that exacerbated
> any
> > REMD problem.
> >
> > Mark
> >
> > Tks.
> >>
> >> On Apr 25, 2013, at 22:40, Mark Abraham <mark.j.abraham at gmail.com>
> wrote:
> >>
> >>> Thanks for the good report. There have been some known issues about the
> >>> timing of coupling stages with respect to various intervals between
> >> GROMACS
> >>> events for some algorithms. There are a lot of fixed problems in 4.5.7
> >> that
> >>> are not specific to REMD, but I have a few lingering doubts about
> whether
> >>> we should be exchanging (scaled) coupling values along with the
> >>> coordinates. (Unlike most REMD implementations, GROMACS swaps the
> >>> coordinates, not the ensemble data.) If you can reproduce those kinds
> of
> >>> symptoms in 4.5.7 (whether or not they then crash) then there looks
> like
> >>> there may be a problem with the REMD implementation that is perhaps
> >> evident
> >>> only with the kind of large time step Martini takes?
> >>>
> >>> Mark
> >>>
> >>>
> >>> On Thu, Apr 25, 2013 at 1:28 PM, XAvier Periole <x.periole at rug.nl>
> >> wrote:
> >>>
> >>>>
> >>>> Hi,
> >>>>
> >>>> I have been recently using the REMD code in gmx-407 and gmx-453 and
> got
> >> a
> >>>> few systems crashing for unclear reasons so far. The main tests I made
> >> are
> >>>> using gmx407 but it is all reproducible with gmx453. The crashing was
> >> also
> >>>> reproduced (not necessarily at the same time point) on several
> >>>> architectures.
> >>>>
> >>>> The system is made of a pair of proteins in a membrane patch and for
> >> which
> >>>> the relative orientation is controlled by non-native
> >> bond/angles/dihedrals
> >>>> to perform an umbrella sampling. I use the MARTINI force field but
> that
> >>>> might not be relevant here.
> >>>>
> >>>> The crashes occur following exchanges that do not seem to occur the
> >>>> correct way and preceded by pressure scaling warnings … indicative of
> a
> >>>> strong destabilisation of the system and eventual explosion. Some
> >>>> information seems to be exchanged inaccurately.
> >>>>
> >>>> Trying to nail down the problem I got stuck and may be some one can
> >> help.
> >>>> I placed a pdf file showing plots of bonded/nonbonded energies,
> >>>> temperatures, box size etc … around an exchange that does not lead to
> a
> >>>> crash (here: md.chem.rug.nl/~periole/remd-issue.pdf). I plotted stuff
> >>>> every step with the temperature colour coded as indicated in the first
> >>>> figure.
> >>>>
> >>>> From the figure it appears that the step right after the exchange
> there
> >> is
> >>>> a huge jump of Potential energy coming from the LJ(SR) part of it.
> >> Although
> >>>> there are some small discontinuities in the progression of the bond
> and
> >>>> angle energy around the exchange they seem to fine. The temperature
> and
> >> box
> >>>> size seem to respond to it a few step latter while the pressure seems
> >> to be
> >>>> affected right away but potentially as the Epot will affect the viral
> >> and
> >>>> thus the Pressure.
> >>>>
> >>>> The other potential clue is that the jumps reduce with the strength of
> >> the
> >>>> pressure coupling. A 1/2 ps tau_p (Berendsen) will lead to a crash
> >> while a
> >>>> 5/10/20 ps won't. Inspection of the time evolution of the Epot, box …
> >>>> indicates that the magnitude of the jumps is reduced and the system ca
> >>>> handle the problem.
> >>>>
> >>>> One additional info since I first posted the problem (delayed by the
> >> file
> >>>> first attached but now given with a link) the problem is accentuated
> >> when
> >>>> the replicas differ in conformation. I am looking at the actual
> >> differences
> >>>> as you'll read this email.
> >>>>
> >>>> That is as far as I could go. Any suggestion is welcome.
> >>>>
> >>>> XAvier.
> >>>> MD-Group / Univ. of Groningen
> >>>> The Netherlands--
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