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You might be experiencing the same thing that was discussed on the
users list in September:<br>
<br>
<a class="moz-txt-link-freetext" href="http://lists.gromacs.org/pipermail/gmx-users/2011-September/064236.html">http://lists.gromacs.org/pipermail/gmx-users/2011-September/064236.html</a><br>
<a class="moz-txt-link-freetext" href="http://lists.gromacs.org/pipermail/gmx-users/2011-September/064237.html">http://lists.gromacs.org/pipermail/gmx-users/2011-September/064237.html</a><br>
<br>
The conclusion there was to use a small nstpcouple (perhaps =1)
during equilibration.<br>
<br>
Chris.<br>
<br>
On 11-10-03 12:53 PM, Miguel Machuqueiro wrote:
<blockquote cite="mid:4E89E8A7.6010706@fc.ul.pt" type="cite">
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<br>
Hi to all developers,<br>
<br>
We have been using GMX here in the group for almost a decade and
we are familiar with almost all versions of the package.<br>
Recently, when testing the newer versions (4.5.x) using Reaction
Field in a simple lysozyme system (4LZT), my system crashed
constantly.<br>
<br>
System: 4LZT (129 a.a.) directly from PDB databank.<br>
Water: ~6250 molecules<br>
GMX: 4.5.x (all versions tested)<br>
ForceField: Gromos 53A6<br>
Long range elect.: RF, RF-nec, GRF or simply "Cutoff" (all with
same fate.. crash!)<br>
Ensemble: NPT or NVT<br>
<br>
So, what do we already know about the problem:<br>
- The crash always starts in the NH bond present in the amides
(main chain or side chains of GLN and ASN). In the stepxxxx.pdb,
we observe the hydrogen jumping out of place.<br>
- The stability of the simulation is dependent on the quality of
the minimization/initialization procedure. Simple/regular
procedures leads to crashs within 10 ns of simulation. More
elaborate protocols of minimization/initialization can delay the
crashs a little longer.<br>
- The system crashes independently of the number of "threads"
used (1-12).<br>
- The instability only leads to crashs when dealing with proteins
>100 a.a.. Simulating a 15 a.a. peptide for over 1 microsecond
does not lead to a crash.<br>
- No problem/crash is observed when using PME.<br>
- No problem/crash is observed when using GMX versions prior to
4.0.7.<br>
<br>
My question is this, what might have happen with the RF code
between versions 4.0.x and 4.5.x that leads to this problem? Or is
there any specific parameter to be used with RF/Cutoff to avoid
these problems?<br>
<br>
Even though RF is not very popular with GMX developers, it has
been essential for the development of our in house Constant-pH MD
method (<a moz-do-not-send="true"
href="http://www.gromacs.org/Documentation/How-tos/Constant_pH_Simulation?highlight=constant+pH">http://www.gromacs.org/Documentation/How-tos/Constant_pH_Simulation</a>).<br>
<br>
On a typical MD run we use the following MDP file, or a similar
one.<br>
<br>
________________<br>
integrator = md<br>
tinit = 0<br>
dt = 0.002<br>
nsteps = 5000000<br>
comm-mode = Linear<br>
nstcomm = 1<br>
nstxout = 0<br>
nstvout = 0<br>
nstfout = 0<br>
nstlog = 5000<br>
nstenergy = 5000<br>
nstxtcout = 5000<br>
xtc-precision = 1000<br>
energygrps = Protein SOL<br>
nstlist = 5<br>
ns_type = grid<br>
pbc = xyz<br>
periodic_molecules = no<br>
rlist = 0.9<br>
coulombtype = Reaction-Field<br>
rcoulomb-switch = 0<br>
rcoulomb = 1.4<br>
epsilon_r = 1<br>
epsilon_rf = 54<br>
vdwtype = Cut-off<br>
rvdw-switch = 0<br>
rvdw = 1.4<br>
DispCorr = No<br>
tcoupl = berendsen<br>
tc-grps = Protein SOL<br>
tau-t = 0.1 0.1<br>
ref-t = 298.15 298.15<br>
Pcoupl = berendsen<br>
Pcoupltype = Isotropic<br>
tau-p = 0.5<br>
compressibility = 4.5e-5<br>
ref-p = 1<br>
refcoord_scaling = No<br>
gen_vel = no<br>
constraints = all-bonds<br>
constraint_algorithm = lincs<br>
lincs-order = 4<br>
lincs-iter = 1<br>
lincs-warnangle = 90<br>
___________________________<br>
<br>
Thank you for any help you can assist us.<br>
<br>
Regards,<br>
Miguel<br>
<br>
<pre class="moz-signature" cols="72">--
============================================
Miguel Machuqueiro
Department of Chemistry and Biochemistry
Faculty of Sciences, University of Lisbon
Campo Grande, Edifício C8 (sala 8.5.47)
1749-016 Lisboa, Portugal
Tel. : +351 217500112 (int.ext.28547)
Mobile: +351 967562285
E-mail: machuque at fc.ul.pt
www1: <a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://webpages.fc.ul.pt/%7Emamachuqueiro">http://webpages.fc.ul.pt/~mamachuqueiro</a>
www2: <a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://intheochem.fc.ul.pt">http://intheochem.fc.ul.pt</a>
______________________________________________
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