[gmx-users] Possible free energy bug? (NOT SOLVED)

Justin A. Lemkul jalemkul at vt.edu
Mon Mar 14 18:47:24 CET 2011



Berk Hess wrote:
> Hi,
> 
> I'm afraid I won't have time to look into this before the 4.5.4 release.
> 
> If you're very lucky valgrind might tell you something.
> 

I'm going to do a bit more digging, but I don't know that this is ultimately a 
Gromacs problem, rather a perfect storm of old compilers, old hardware, and 
somehow the free energy code not playing nicely in an unfavorable environment. 
If Gromacs can be made more robust, that would be great, but otherwise, I don't 
know that this is something worth investing much of your time on.  I have 
determined the following:

1. Serial runs work fine
2. Running on newer hardware (an x86_64 CPU/GPU cluster) with threading works
3. OpenMPI-1.2.3 on PowerPC with GCC-4.4.5 + FFTW-3.2.2 fails
4. OpenMPI-1.4.3 on PowerPC with GCC-4.4.5 + FFTW-3.2.2 works

I'm wondering if it's really been OpenMPI-1.2.3 all along that's the problem, 
somehow causing Gromacs to fail via LINCS errors when data are not passed 
properly or something.

If I can tease something out using debugging modes, I will report back. 
Otherwise, this is probably a low-priority issue for anyone to try to sort out, 
but hopefully the information I've posted here will be useful to anyone else who 
might come across it.

-Justin

> Berk
> 
>  > Date: Sat, 12 Mar 2011 20:18:34 -0500
>  > From: jalemkul at vt.edu
>  > To: gmx-users at gromacs.org
>  > Subject: Re: [gmx-users] Possible free energy bug? (NOT SOLVED)
>  >
>  >
>  > Hi All,
>  >
>  > Unfortunately, my positive news was a false alarm. Intermediate 
> values of
>  > lambda are sporadically failing at different times. Some jobs exit at 
> time
>  > zero, others last somewhat longer (several hundred ps) before 
> failing. I'm
>  > going to keep working on the suggestions I got before about 
> compilation options
>  > and such, but for now I will post the error output to see if it 
> provides any
>  > clues about what's wrong:
>  >
>  > Warning: Only triclinic boxes with the first vector parallel to the 
> x-axis and
>  > the second vector in the xy-plane are supported.
>  > Warning: Only triclinic boxes with the first vector parallel to the 
> x-axis and
>  > the second vector in the xy-plane are supported.
>  > Box (3x3):
>  > Box[ 0]={ nan, 0.00000e+00, 0.00000e+00}
>  > Box[ 1]={ nan, nan, nan}
>  > Box[ 2]={ nan, nan, nan}
>  > Can not fix pbc.
>  > Warning: Only triclinic boxes with the first vector parallel to the 
> x-axis and
>  > the second vector in the xy-plane are supported.
>  > Box (3x3):
>  > Box[ 0]={ nan, 0.00000e+00, 0.00000e+00}
>  > Box[ 1]={ nan, nan, nan}
>  > Box[ 2]={ nan, nan, nan}
>  > Can not fix pbc.
>  > Box (3x3):
>  > Box[ 0]={ nan, 0.00000e+00, 0.00000e+00}
>  > Box[ 1]={ nan, nan, nan}
>  > Box[ 2]={ nan, nan, nan}
>  > Can not fix pbc.
>  > Warning: Only triclinic boxes with the first vector parallel to the 
> x-axis and
>  > the second vector in the xy-plane are supported.
>  > Box (3x3):
>  > Box[ 0]={ nan, 0.00000e+00, 0.00000e+00}
>  > Box[ 1]={ nan, nan, nan}
>  > Box[ 2]={ nan, nan, nan}
>  > Can not fix pbc.
>  > [n921:01432] *** Process received signal ***
>  > [n921:01432] Signal: Segmentation fault (11)
>  > [n921:01432] Signal code: Address not mapped (1)
>  > [n921:01432] Failing at address: 0xfffffffe10af11c0
>  > [n921:01432] [ 0] [0x100428]
>  > [n921:01432] [ 1] [0xfffffcc01f4]
>  > [n921:01432] [ 2]
>  > 
> /home/rdiv1001/gromacs-4.5.3-linux_gcc445_fftw322/bin/mdrun_4.5.3_gcc_mpi(gmx_pme_do-0x51df30) 
> 
>  > [0x1010c0e8]
>  > [n921:01432] [ 3]
>  > 
> /home/rdiv1001/gromacs-4.5.3-linux_gcc445_fftw322/bin/mdrun_4.5.3_gcc_mpi(do_force_lowlevel-0x560cd0) 
> 
>  > [0x100c88c8]
>  > [n921:01432] [ 4]
>  > 
> /home/rdiv1001/gromacs-4.5.3-linux_gcc445_fftw322/bin/mdrun_4.5.3_gcc_mpi(do_force-0x50b084) 
> 
>  > [0x1011f594]
>  > [n921:01432] [ 5]
>  > 
> /home/rdiv1001/gromacs-4.5.3-linux_gcc445_fftw322/bin/mdrun_4.5.3_gcc_mpi(do_md-0x5bbb78) 
> 
>  > [0x1006cac0]
>  > [n921:01432] [ 6]
>  > 
> /home/rdiv1001/gromacs-4.5.3-linux_gcc445_fftw322/bin/mdrun_4.5.3_gcc_mpi(mdrunner-0x5c26f8) 
> 
>  > [0x10065e98]
>  > [n921:01432] [ 7]
>  > 
> /home/rdiv1001/gromacs-4.5.3-linux_gcc445_fftw322/bin/mdrun_4.5.3_gcc_mpi(main-0x5b7964) 
> 
>  > [0x10070cec]
>  > [n921:01432] [ 8] /lib64/libc.so.6 [0x80aaed8858]
>  > [n921:01432] [ 9] /lib64/libc.so.6(__libc_start_main-0x1471f8) 
> [0x80aaed8ad0]
>  > [n921:01432] *** End of error message ***
>  >
>  > I have not yet compiled with debugging enabled, but I can if that 
> will be useful.
>  >
>  > -Justin
>  >
>  > Justin A. Lemkul wrote:
>  > >
>  > > Hi All,
>  > >
>  > > I believe I have a resolution to all of this. It comes down to
>  > > compilers and FFTW. I had always used the same compilers to build all
>  > > my Gromacs versions (gcc-4.2.2 on Linux, gcc-3.3 on OSX) with the same
>  > > version of FFTW (3.0.1), primarily for reasons of continuity. Bug 715
>  > > that I posted before was due to a problem with FFTW, not Gromacs;
>  > > upgrading to 3.2.2 solves the issue. As well, the combination of
>  > > gcc-4.4.5 + FFTW 3.2.2 allows for successful free energy runs in my
>  > > tests thus far on Linux. Dependency issues on the OS X partition
>  > > prevent me from doing any upgrades, so we're out of luck there,
>  > > unfortunately. I will report back if any other weird behavior results,
>  > > but I believe the problem is solved.
>  > >
>  > > I am no compiler/library guru, but it would seem to me that we've
>  > > reached a point where certain minimum versions must be required for
>  > > certain prerequisites. I would suggest that prior to the next release,
>  > > we come up with a list of what should be considered stable minimum
>  > > requirements (compiler versions, FFTW, anything else) to post on the
>  > > website and perhaps the manual. As it stands now, the prerequisites 
> for
>  > > installation would seem to be satisfied by any C compiler and any
>  > > version of FFTW. Gromacs happily compiles under most conditions, but
>  > > shows some weird behavior if one is not using optimal dependencies.
>  > >
>  > > Thanks to all for their input!
>  > >
>  > > -Justin
>  > >
>  > > Justin A. Lemkul wrote:
>  > >>
>  > >>
>  > >> Michael Shirts wrote:
>  > >>> Hi, all-
>  > >>>
>  > >>> Have you tried running
>  > >>>
>  > >>> constraints = hbonds?
>  > >>>
>  > >>> That might eliminate some of the constraint issues. Much less likely
>  > >>> for LINCS to break or have DD issues if only the hbonds are
>  > >>> constrained. 2 fs is not that big a deal for the heteroatom bonds.
>  > >>>
>  > >>
>  > >> I haven't yet, but I'll add it to my to-do list. I was trying to keep
>  > >> as many things consistent between my 3.3.3 and 4.5.3 input files as
>  > >> possible, so I could diagnose any issues, but at this point, anything
>  > >> is worth a shot.
>  > >>
>  > >> Thanks!
>  > >>
>  > >> -Justin
>  > >>
>  > >>> Best,
>  > >>> Michael
>  > >>>
>  > >>> On Thu, Mar 10, 2011 at 8:04 PM, Justin A. Lemkul <jalemkul at vt.edu>
>  > >>> wrote:
>  > >>>> Hi Matt,
>  > >>>>
>  > >>>> Thanks for the extensive explanation and tips. I'll work through
>  > >>>> things and
>  > >>>> report back. It will take a while to get things going through
>  > >>>> (unless one
>  > >>>> of the early solutions works!) since I have no admin access to
>  > >>>> install new
>  > >>>> compilers, libraries, etc. and for some reason the only thing I can
>  > >>>> ever get
>  > >>>> to work in my home directory is Gromacs itself. The joys of an aging
>  > >>>> cluster.
>  > >>>>
>  > >>>> We recently got access to gcc-4.4.5 on Linux, but we're stuck with
>  > >>>> 3.3 on OS
>  > >>>> X, so there's at least a bit of hope for one partition.
>  > >>>>
>  > >>>> Thanks again.
>  > >>>>
>  > >>>> -Justin
>  > >>>>
>  > >>>> Matthew Zwier wrote:
>  > >>>>> Hi Justin,
>  > >>>>>
>  > >>>>> I should have specified that the segfault happened for us after 
> we got
>  > >>>>> similar warnings and errors (DD and/or LINCS), so the segfault may
>  > >>>>> have been tangential. Given that everything about your system 
> worked
>  > >>>>> before GROMACS 4.5, it's possible that your older compilers are
>  > >>>>> generating code that's incompatible with the GROMACS assembly loops
>  > >>>>> (which you are likely running with, as they are the default 
> option on
>  > >>>>> most mainstream processors). The bug you mentioned in your original
>  > >>>>> post also has my antennae twitching about bad machine code.
>  > >>>>>
>  > >>>>> If that's indeed happening, it's almost certainly some bizarre
>  > >>>>> alignment issue, something like half of a float is getting 
> overwritten
>  > >>>>> on the way into or out of the assembly code, which corruption would
>  > >>>>> trigger the results you describe. It's also distantly possible that
>  > >>>>> GROMACS is working fine, but your copy of FFTW or BLAS/LAPACK (more
>  > >>>>> likely the latter) has alignment problems. One final possibility
>  > >>>>> (which would explain the failure on YellowDog but unfortunately not
>  > >>>>> the failure on OS X) is that GCC is generating badly-aligned 
> code for
>  > >>>>> auto-vectorized Altivec loops, which is still a problem for Intel's
>  > >>>>> SIMD instructions on 32-bit x86 architectures even with GCC 
> 4.4. I've
>  > >>>>> also observed MPI gather/reduce operations to foul up alignment (or
>  > >>>>> rigidly enforce it where badly compiled code is relying on broken
>  > >>>>> alignment) under exceedingly rare circumstances, usually involving
>  > >>>>> different libraries compiled with different compilers (which is
>  > >>>>> generally a bad idea for scientific code anyway).
>  > >>>>>
>  > >>>>> Okay...so all of that said, there are a few things to try:
>  > >>>>>
>  > >>>>> 1) Recompile GROMACS using -O2 instead of -O3; that'll turn off the
>  > >>>>> automatic vectorizer (on Yellow Dog) and various other relatively
>  > >>>>> risky optimizations (on both platforms). CFLAGS="-O2 
> -march=powerpc"
>  > >>>>> in the environment AND on the configure command line would do that.
>  > >>>>> Check your build logs to make sure it took, though, because if you
>  > >>>>> don't do it exactly right, configure will ignore your 
> directives and
>  > >>>>> merrily set up GROMACS to compile with -O3, which is the most 
> likely
>  > >>>>> culprit for badly-aligned code.
>  > >>>>>
>  > >>>>> 2) Recompile GROMACS specifying a forced alignment flag. I have no
>  > >>>>> experience with PowerPC, but -malign-natural and -malign-power look
>  > >>>>> like good initial guesses. That's probably going to cause more
>  > >>>>> problems than it solves, but if you have a screwy BLAS/LAPACK 
> or MPI,
>  > >>>>> it might help. I only suggest it because if you've already 
> tried #1,
>  > >>>>> it will only take another half hour or hour of your time to 
> recompile
>  > >>>>> GROMACS again. Other than that, tinkering with alignment flags is a
>  > >>>>> really easy way to REALLY break code, so you might consider 
> skipping
>  > >>>>> this and moving straight on to #3.
>  > >>>>>
>  > >>>>> 3) Snag GCC 4.4.4 or 4.4.5 and compile it, and use that to compile
>  > >>>>> GROMACS, again with -O2. GCC takes forever to compile, but beyond
>  > >>>>> that, it's not as difficult as it could be. Nothing preventing you
>  > >>>>> from installing it in your home directory, either, assuming you set
>  > >>>>> PATH and LD_LIBRARY_PATH (or DYLD_LIBRARY_PATH on OS X) 
> properly. You
>  > >>>>> might need to snag a new copy of binutils as well, if gcc 
> refuses to
>  > >>>>> compile with the system ld. This option would also probably get you
>  > >>>>> threading, since you certainly have hardware support for it.
>  > >>>>>
>  > >>>>> 4) Rebuild your entire GROMACS stack, including FFTW, BLAS/LAPACK,
>  > >>>>> MPI, and GROMACS itself with the same compiler (preferably GCC from
>  > >>>>> #3) and the same compiler options (which again should be -O2, and
>  > >>>>> definitely NOT any sort of alignment flag). Put them in their own
>  > >>>>> tree (like "/opt/sci"), and definitely not in /usr (which is 
> generally
>  > >>>>> managed by the system) or /usr/local (which tends to accumulate
>  > >>>>> cruft). ATLAS is a good choice for BLAS, and there are 
> directions on
>  > >>>>> the ATLAS website for building a complete and optimized LAPACK 
> based
>  > >>>>> on BLAS.
>  > >>>>>
>  > >>>>> In practice, I've found I've had to do #4 for every piece of
>  > >>>>> scientific software our group uses, because pretty much nothing 
> works
>  > >>>>> right with OS-installed versions of compilers, BLAS/LAPACK, and 
> MPI.
>  > >>>>> It takes forever, and it pretty much defines the phrase "learning
>  > >>>>> experience," but it also essentially *never* breaks once it works
>  > >>>>> (because OS updates never overwrite anything you've hand-tuned 
> to run
>  > >>>>> correctly). But...with luck option #1 will fix things quickly 
> enough
>  > >>>>> to get you running without devoting two days to rebuilding your
>  > >>>>> software stack from scratch.
>  > >>>>>
>  > >>>>> Hope that helps,
>  > >>>>> Matt Z.
>  > >>>>>
>  > >>>>>
>  > >>>>> On Thu, Mar 10, 2011 at 8:54 PM, Justin A. Lemkul 
> <jalemkul at vt.edu>
>  > >>>>> wrote:
>  > >>>>>> Hi Matt,
>  > >>>>>>
>  > >>>>>> Thanks for the reply. I can't trace the problem to a specific
>  > >>>>>> compiler.
>  > >>>>>> We
>  > >>>>>> have a PowerPC cluster with two partitions - one running Mac OS X
>  > >>>>>> 10.3
>  > >>>>>> with
>  > >>>>>> gcc-3.3, the other running YellowDog Linux with gcc-4.2.2. The
>  > >>>>>> problem
>  > >>>>>> happens on both partitions. There are no seg faults, the runs
>  > >>>>>> just exit
>  > >>>>>> (MPI_ABORT) after the fatal error (either "too many LINCS
>  > >>>>>> warnings" or
>  > >>>>>> the
>  > >>>>>> DD-related error I posted before).
>  > >>>>>>
>  > >>>>>> We are using MPI: mpich-1.2.5 on OSX and OpenMPI-1.2.3 on Linux.
>  > >>>>>> All of
>  > >>>>>> the
>  > >>>>>> above has been the same since my successful 3.3.3 TI 
> calculations (as
>  > >>>>>> well
>  > >>>>>> as all of my simulations with Gromacs, ever). Our hardware and
>  > >>>>>> compilers
>  > >>>>>> are somewhat (very) outdated so threading is not supported, we
>  > >>>>>> always use
>  > >>>>>> MPI.
>  > >>>>>>
>  > >>>>>> Gromacs was compiled in single precision using standard options
>  > >>>>>> through
>  > >>>>>> autoconf. The cmake build system still does not work on our
>  > >>>>>> cluster due
>  > >>>>>> to
>  > >>>>>> several outstanding bugs.
>  > >>>>>>
>  > >>>>>> -Justin
>  > >>>>>>
>  > >>>>>> Matthew Zwier wrote:
>  > >>>>>>> Dear Justin,
>  > >>>>>>>
>  > >>>>>>> We recently experienced a similar problem (LINCS errors, 
> step*.pdb
>  > >>>>>>> files), and then GROMACS usually segfaulted. The cause was a
>  > >>>>>>> miscompiled copy of GROMACS. Another member of our group had
>  > >>>>>>> compiled
>  > >>>>>>> GROMACS on an Intel Core2 quad (gcc -march=core2) and tried to
>  > >>>>>>> run the
>  > >>>>>>> copy without modification on an AMD Magny Cours machine.
>  > >>>>>>> Recompilation with the correct subarchitecture type
>  > >>>>>>> (-march=amdfam10)
>  > >>>>>>> fixed the problem. Don't really know why it didn't die with
>  > >>>>>>> SIGILL or
>  > >>>>>>> SIGBUS instead of SIGSEGV, but that's probably a question for the
>  > >>>>>>> hardware gurus.
>  > >>>>>>>
>  > >>>>>>> So...are you observing segfaults? What compiler are you using
>  > >>>>>>> (and on
>  > >>>>>>> what OS)? What were the compilation parameters for 4.5.3? Also,
>  > >>>>>>> are
>  > >>>>>>> you really running across nodes with MPI, or running on the same
>  > >>>>>>> node
>  > >>>>>>> with MPI?
>  > >>>>>>>
>  > >>>>>>> Cheers,
>  > >>>>>>> Matt Zwier
>  > >>>>>>>
>  > >>>>>>> On Thu, Mar 10, 2011 at 1:55 PM, Justin A. Lemkul 
> <jalemkul at vt.edu>
>  > >>>>>>> wrote:
>  > >>>>>>>> Hi All,
>  > >>>>>>>>
>  > >>>>>>>> I've been troubleshooting a problem for some time now and I
>  > >>>>>>>> wanted to
>  > >>>>>>>> report
>  > >>>>>>>> it here and solicit some feedback before I submit a bug report
>  > >>>>>>>> to see
>  > >>>>>>>> if
>  > >>>>>>>> there's anything else I can try.
>  > >>>>>>>>
>  > >>>>>>>> Here's the situation: I ran some free energy calculations
>  > >>>>>>>> (thermodynamic
>  > >>>>>>>> integration) a long time ago using version 3.3.3 to 
> determine the
>  > >>>>>>>> hydration
>  > >>>>>>>> free energy of a series of small molecules. Results were good
>  > >>>>>>>> and they
>  > >>>>>>>> ended up as part of a paper, so I'm trying to reproduce the
>  > >>>>>>>> methodology
>  > >>>>>>>> with
>  > >>>>>>>> 4.5.3 (using BAR) to see if I understand the workflow
>  > >>>>>>>> completely. The
>  > >>>>>>>> problem is my systems are crashing. The runs simply stop 
> randomly
>  > >>>>>>>> (usually
>  > >>>>>>>> within a few hundred ps) with lots of LINCS warnings and 
> step*.pdb
>  > >>>>>>>> files
>  > >>>>>>>> being written.
>  > >>>>>>>>
>  > >>>>>>>> I know the parameters are good, and produce stable 
> trajectories,
>  > >>>>>>>> since
>  > >>>>>>>> I
>  > >>>>>>>> spent months on them some years ago. The system prep is steepest
>  > >>>>>>>> descents
>  > >>>>>>>> EM
>  > >>>>>>>> to Fmax < 100 (always achieved), NVT at 298 K for 100 ps, 
> NPT at
>  > >>>>>>>> 298K/1
>  > >>>>>>>> bar
>  > >>>>>>>> for 100 ps, then 5 ns of data collection under NPT conditions.
>  > >>>>>>>> Here's
>  > >>>>>>>> the
>  > >>>>>>>> rundown of what I'm seeing:
>  > >>>>>>>>
>  > >>>>>>>> 1. All LJ transformations work fine. The problem only comes 
> when I
>  > >>>>>>>> have
>  > >>>>>>>> a
>  > >>>>>>>> molecule with full LJ interaction and I am "charging" it (i.e.,
>  > >>>>>>>> introducing
>  > >>>>>>>> charges to the partially-interacting species).
>  > >>>>>>>>
>  > >>>>>>>> 2. Simulations at lambda=1 (full interaction) work fine.
>  > >>>>>>>>
>  > >>>>>>>> 3. Simulations with the free energy code off entirely work fine
>  > >>>>>>>> under
>  > >>>>>>>> all
>  > >>>>>>>> conditions.
>  > >>>>>>>>
>  > >>>>>>>> 4. I cannot run in serial due to
>  > >>>>>>>> http://redmine.gromacs.org/issues/715.
>  > >>>>>>>> The
>  > >>>>>>>> bug seems to affect other systems and is not specifically
>  > >>>>>>>> related to my
>  > >>>>>>>> free
>  > >>>>>>>> energy calculations.
>  > >>>>>>>>
>  > >>>>>>>> 5. Running with DD fails because my system is relatively small
>  > >>>>>>>> (more on
>  > >>>>>>>> this
>  > >>>>>>>> in a moment).
>  > >>>>>>>>
>  > >>>>>>>> 6. Running with mdrun -pd 2 works, but mdrun -pd 4 crashes 
> for any
>  > >>>>>>>> value
>  > >>>>>>>> of
>  > >>>>>>>> lambda != 1.
>  > >>>>>>>>
>  > >>>>>>>> 7. I created a larger system (instead of a 3x3x3-nm cube of
>  > >>>>>>>> water with
>  > >>>>>>>> my
>  > >>>>>>>> molecule, I used 4x4x4) and ran on 4 CPU's with DD (lambda = 0,
>  > >>>>>>>> i.e.
>  > >>>>>>>> full
>  > >>>>>>>> vdW, no intermolecular Coulombic interactions - .mdp file is
>  > >>>>>>>> below).
>  > >>>>>>>> This
>  > >>>>>>>> run also crashed with some warnings about DD cell size:
>  > >>>>>>>>
>  > >>>>>>>> DD load balancing is limited by minimum cell size in dimension X
>  > >>>>>>>> DD step 329999 vol min/aver 0.748! load imb.: force 31.5%
>  > >>>>>>>>
>  > >>>>>>>> ...and then the actual crash:
>  > >>>>>>>>
>  > >>>>>>>> -------------------------------------------------------
>  > >>>>>>>> Program mdrun_4.5.3_gcc_mpi, VERSION 4.5.3
>  > >>>>>>>> Source code file: domdec_con.c, line: 693
>  > >>>>>>>>
>  > >>>>>>>> Fatal error:
>  > >>>>>>>> DD cell 0 0 0 could only obtain 14 of the 15 atoms that are
>  > >>>>>>>> connected
>  > >>>>>>>> via
>  > >>>>>>>> constraints from the neighboring cells. This probably means your
>  > >>>>>>>> constraint
>  > >>>>>>>> lengths are too long compared to the domain decomposition cell
>  > >>>>>>>> size.
>  > >>>>>>>> Decrease the number of domain decomposition grid cells or
>  > >>>>>>>> lincs-order
>  > >>>>>>>> or
>  > >>>>>>>> use
>  > >>>>>>>> the -rcon option of mdrun.
>  > >>>>>>>> For more information and tips for troubleshooting, please 
> check the
>  > >>>>>>>> GROMACS
>  > >>>>>>>> website at http://www.gromacs.org/Documentation/Errors
>  > >>>>>>>> -------------------------------------------------------
>  > >>>>>>>>
>  > >>>>>>>> Watching the trajectory doesn't seem to give any useful
>  > >>>>>>>> information.
>  > >>>>>>>> The
>  > >>>>>>>> small molecule of interest is at a periodic boundary when 
> the crash
>  > >>>>>>>> happens,
>  > >>>>>>>> but there are several crosses prior to the crash without
>  > >>>>>>>> incident, so I
>  > >>>>>>>> don't know if the issue is related to PBC or not, but it 
> appears
>  > >>>>>>>> not.
>  > >>>>>>>>
>  > >>>>>>>> 8. I initially thought the problem might be related to the
>  > >>>>>>>> barostat,
>  > >>>>>>>> but
>  > >>>>>>>> switching from P-R to Berendsen does not alleviate the 
> problem, nor
>  > >>>>>>>> does
>  > >>>>>>>> increasing tau_p (tested 0.5, 1.0, 2.0, and 5.0 - all crash).
>  > >>>>>>>> Longer
>  > >>>>>>>> tau_p
>  > >>>>>>>> simply delays the crash, but does not prevent it.
>  > >>>>>>>>
>  > >>>>>>>> So after all that, I'm wondering if (1) anyone has seen the
>  > >>>>>>>> same, or
>  > >>>>>>>> (2)
>  > >>>>>>>> if
>  > >>>>>>>> there's anything else I can try (environment variables, hidden
>  > >>>>>>>> tricks,
>  > >>>>>>>> etc)
>  > >>>>>>>> that I can use to get to the bottom of this before I give up 
> and
>  > >>>>>>>> file a
>  > >>>>>>>> bug
>  > >>>>>>>> report.
>  > >>>>>>>>
>  > >>>>>>>> If you made it this far, thanks for reading my novel and 
> hopefully
>  > >>>>>>>> someone
>  > >>>>>>>> can give me some ideas. The .mdp file I'm using is below, but
>  > >>>>>>>> it is
>  > >>>>>>>> just
>  > >>>>>>>> one of many that I've tried. In theory, it should work, 
> since the
>  > >>>>>>>> parameters are the same as my successful 3.3.3 runs, with the
>  > >>>>>>>> exception
>  > >>>>>>>> of
>  > >>>>>>>> the new free energy features in 4.5.3 and obvious keyword 
> changes
>  > >>>>>>>> related
>  > >>>>>>>> to
>  > >>>>>>>> the difference in version.
>  > >>>>>>>>
>  > >>>>>>>> -Justin
>  > >>>>>>>>
>  > >>>>>>>> --- .mdp file ---
>  > >>>>>>>>
>  > >>>>>>>> ; Run control
>  > >>>>>>>> integrator = sd ; Langevin dynamics
>  > >>>>>>>> tinit = 0
>  > >>>>>>>> dt = 0.002
>  > >>>>>>>> nsteps = 2500000 ; 5 ns
>  > >>>>>>>> nstcomm = 100
>  > >>>>>>>> ; Output control
>  > >>>>>>>> nstxout = 500
>  > >>>>>>>> nstvout = 500
>  > >>>>>>>> nstfout = 0
>  > >>>>>>>> nstlog = 500
>  > >>>>>>>> nstenergy = 500
>  > >>>>>>>> nstxtcout = 0
>  > >>>>>>>> xtc-precision = 1000
>  > >>>>>>>> ; Neighborsearching and short-range nonbonded interactions
>  > >>>>>>>> nstlist = 5
>  > >>>>>>>> ns_type = grid
>  > >>>>>>>> pbc = xyz
>  > >>>>>>>> rlist = 0.9
>  > >>>>>>>> ; Electrostatics
>  > >>>>>>>> coulombtype = PME
>  > >>>>>>>> rcoulomb = 0.9
>  > >>>>>>>> ; van der Waals
>  > >>>>>>>> vdw-type = cutoff
>  > >>>>>>>> rvdw = 1.4
>  > >>>>>>>> ; Apply long range dispersion corrections for Energy and 
> Pressure
>  > >>>>>>>> DispCorr = EnerPres
>  > >>>>>>>> ; Spacing for the PME/PPPM FFT grid
>  > >>>>>>>> fourierspacing = 0.12
>  > >>>>>>>> ; EWALD/PME/PPPM parameters
>  > >>>>>>>> pme_order = 4
>  > >>>>>>>> ewald_rtol = 1e-05
>  > >>>>>>>> epsilon_surface = 0
>  > >>>>>>>> optimize_fft = no
>  > >>>>>>>> ; Temperature coupling
>  > >>>>>>>> ; tcoupl is implicitly handled by the sd integrator
>  > >>>>>>>> tc_grps = system
>  > >>>>>>>> tau_t = 1.0
>  > >>>>>>>> ref_t = 298
>  > >>>>>>>> ; Pressure coupling is on for NPT
>  > >>>>>>>> Pcoupl = Berendsen
>  > >>>>>>>> tau_p = 2.0
>  > >>>>>>>> compressibility = 4.5e-05
>  > >>>>>>>> ref_p = 1.0
>  > >>>>>>>> ; Free energy control stuff
>  > >>>>>>>> free_energy = yes
>  > >>>>>>>> init_lambda = 0.00
>  > >>>>>>>> delta_lambda = 0
>  > >>>>>>>> foreign_lambda = 0.05
>  > >>>>>>>> sc-alpha = 0
>  > >>>>>>>> sc-power = 1.0
>  > >>>>>>>> sc-sigma = 0
>  > >>>>>>>> couple-moltype = MOR ; name of moleculetype to
>  > >>>>>>>> couple
>  > >>>>>>>> couple-lambda0 = vdw ; vdW interactions
>  > >>>>>>>> couple-lambda1 = vdw-q ; turn on everything
>  > >>>>>>>> couple-intramol = no
>  > >>>>>>>> dhdl_derivatives = yes ; this line (and the next
>  > >>>>>>>> two) are
>  > >>>>>>>> defaults
>  > >>>>>>>> separate_dhdl_file = yes ; included only for pedantry
>  > >>>>>>>> nstdhdl = 10
>  > >>>>>>>> ; Do not generate velocities
>  > >>>>>>>> gen_vel = no
>  > >>>>>>>> ; options for bonds
>  > >>>>>>>> constraints = all-bonds
>  > >>>>>>>> ; Type of constraint algorithm
>  > >>>>>>>> constraint-algorithm = lincs
>  > >>>>>>>> ; Constrain the starting configuration
>  > >>>>>>>> ; since we are continuing from NPT
>  > >>>>>>>> continuation = yes
>  > >>>>>>>> ; Highest order in the expansion of the constraint coupling 
> matrix
>  > >>>>>>>> lincs-order = 4
>  > >>>>>>>>
>  > >>>>>>>>
>  > >>>>>>>> --
>  > >>>>>>>> ========================================
>  > >>>>>>>>
>  > >>>>>>>> Justin A. Lemkul
>  > >>>>>>>> Ph.D. Candidate
>  > >>>>>>>> ICTAS Doctoral Scholar
>  > >>>>>>>> MILES-IGERT Trainee
>  > >>>>>>>> Department of Biochemistry
>  > >>>>>>>> Virginia Tech
>  > >>>>>>>> Blacksburg, VA
>  > >>>>>>>> jalemkul[at]vt.edu | (540) 231-9080
>  > >>>>>>>> http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
>  > >>>>>>>>
>  > >>>>>>>> ========================================
>  > >>>>>>>> --
>  > >>>>>>>> gmx-users mailing list gmx-users at gromacs.org
>  > >>>>>>>> http://lists.gromacs.org/mailman/listinfo/gmx-users
>  > >>>>>>>> Please search the archive at
>  > >>>>>>>> http://www.gromacs.org/Support/Mailing_Lists/Search before 
> posting!
>  > >>>>>>>> Please don't post (un)subscribe requests to the list. Use 
> the www
>  > >>>>>>>> interface
>  > >>>>>>>> or send it to gmx-users-request at gromacs.org.
>  > >>>>>>>> Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
>  > >>>>>>>>
>  > >>>>>> --
>  > >>>>>> ========================================
>  > >>>>>>
>  > >>>>>> Justin A. Lemkul
>  > >>>>>> Ph.D. Candidate
>  > >>>>>> ICTAS Doctoral Scholar
>  > >>>>>> MILES-IGERT Trainee
>  > >>>>>> Department of Biochemistry
>  > >>>>>> Virginia Tech
>  > >>>>>> Blacksburg, VA
>  > >>>>>> jalemkul[at]vt.edu | (540) 231-9080
>  > >>>>>> http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
>  > >>>>>>
>  > >>>>>> ========================================
>  > >>>>>> --
>  > >>>>>> gmx-users mailing list gmx-users at gromacs.org
>  > >>>>>> http://lists.gromacs.org/mailman/listinfo/gmx-users
>  > >>>>>> Please search the archive at
>  > >>>>>> http://www.gromacs.org/Support/Mailing_Lists/Search before 
> posting!
>  > >>>>>> Please don't post (un)subscribe requests to the list. Use the www
>  > >>>>>> interface
>  > >>>>>> or send it to gmx-users-request at gromacs.org.
>  > >>>>>> Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
>  > >>>>>>
>  > >>>> --
>  > >>>> ========================================
>  > >>>>
>  > >>>> Justin A. Lemkul
>  > >>>> Ph.D. Candidate
>  > >>>> ICTAS Doctoral Scholar
>  > >>>> MILES-IGERT Trainee
>  > >>>> Department of Biochemistry
>  > >>>> Virginia Tech
>  > >>>> Blacksburg, VA
>  > >>>> jalemkul[at]vt.edu | (540) 231-9080
>  > >>>> http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
>  > >>>>
>  > >>>> ========================================
>  > >>>> --
>  > >>>> gmx-users mailing list gmx-users at gromacs.org
>  > >>>> http://lists.gromacs.org/mailman/listinfo/gmx-users
>  > >>>> Please search the archive at
>  > >>>> http://www.gromacs.org/Support/Mailing_Lists/Search before posting!
>  > >>>> Please don't post (un)subscribe requests to the list. Use the www
>  > >>>> interface
>  > >>>> or send it to gmx-users-request at gromacs.org.
>  > >>>> Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
>  > >>>>
>  > >>>
>  > >>
>  > >
>  >
>  > --
>  > ========================================
>  >
>  > Justin A. Lemkul
>  > Ph.D. Candidate
>  > ICTAS Doctoral Scholar
>  > MILES-IGERT Trainee
>  > Department of Biochemistry
>  > Virginia Tech
>  > Blacksburg, VA
>  > jalemkul[at]vt.edu | (540) 231-9080
>  > http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
>  >
>  > ========================================
>  > --
>  > gmx-users mailing list gmx-users at gromacs.org
>  > http://lists.gromacs.org/mailman/listinfo/gmx-users
>  > Please search the archive at 
> http://www.gromacs.org/Support/Mailing_Lists/Search before posting!
>  > Please don't post (un)subscribe requests to the list. Use the
>  > www interface or send it to gmx-users-request at gromacs.org.
>  > Can't post? Read http://www.gromacs.org/Support/Mailing_Lists

-- 
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

========================================



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