Thank you both for your replies. I currently have another ionic liquid running just fine on the same gromacs build (compiled the tpr file yesterday), so I am reluctant to conclude that the problem is with the linking. Please let me know if you disagree. <div>
The force field I am using was published in 2004 and has been validated by another group. I have double and triple checked my itp files to make sure they match the force field, but it's possible there are still some errors there. </div>
<div>I agree that this is very strange and feel that there must be something fundamentally wrong in the mdp file or deeper. I have included my mdp file below.</div><div><br></div><div><div>title = PMP+TFN</div>
<div>cpp = /lib/cpp</div><div>constraints = hbonds</div><div>integrator = md</div><div>dt = 0.002 ; ps !</div><div>nsteps = 10000000 ; total 20 ns</div>
<div>nstcomm = 10</div><div>nstxout = 50000</div><div>nstvout = 50000</div><div>nstfout = 0</div><div>nstlog = 5000</div><div>nstenergy = 5000</div>
<div>nstxtcout = 25000</div><div>nstlist = 10</div><div>ns_type = grid</div><div>pbc = xyz</div><div>coulombtype = PME</div><div>vdwtype = Cut-off</div>
<div>rlist = 1.2</div><div>rcoulomb = 1.2</div><div>rvdw = 1.2</div><div>fourierspacing = 0.12</div><div>pme_order = 4</div><div>ewald_rtol = 1e-5</div>
<div>; Berendsen temperature coupling is on in two groups</div><div>Tcoupl = v-rescale</div><div>tc_grps = PMP TFN </div><div>tau_t = 0.2 0.2 </div><div>ref_t = 300 300</div>
<div>nsttcouple = 1</div><div>; Energy monitoring</div><div>energygrps = PMP TFN</div><div>; Isotropic pressure coupling is now on</div><div>Pcoupl = berendsen</div><div>pcoupltype = isotropic</div>
<div>tau_p = 2.0</div><div>ref_p = 1.0</div><div>compressibility = 4.5e-5</div><div><br></div><div>; Generate velocites is on at 300 K.</div><div>gen_vel = yes</div><div>gen_temp = 300.0</div>
<div>gen_seed = -1</div><div><br></div><div><br><div class="gmail_quote">On Fri, Feb 24, 2012 at 12:17 AM, Dommert Florian <span dir="ltr"><<a href="mailto:dommert@icp.uni-stuttgart.de">dommert@icp.uni-stuttgart.de</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On Thu, 2012-02-23 at 13:35 -0700, Denny Frost wrote:<br>
> Dear all,<br>
> I am trying to equilibrate a solvent of pure ionic liquid. The system<br>
> keeps exploding (after 2-5 ns) and I am not sure why, though I believe<br>
> coulombic interactions are to blame. This is because the Coul-SR term<br>
> is negative, but the Coul. recip term is very positive throughout the<br>
> entire run (giving the entire system a positive potential energy). I<br>
> think this means that the short-range electrostatics are okay, but the<br>
> long range electrostatics (calculated with PME) are not. Does anybody<br>
> have any suggestions as to why this would happen? I have used the<br>
> exact same PME input parameters for another ionic liquid that works<br>
> just fine. They are listed below.<br>
><br>
><br>
> rcoulomb = 1.2<br>
> fourierspacing = 0.12<br>
> pme_order = 4<br>
> ewald_rtol = 1e-5<br>
><br>
<br>
</div></div>Depends on the force field you are using. Perhaps it ist not validated<br>
for the ionic liquid you want to study. It is especially strange, that<br>
it takes so long for your system to blow up.<br>
<br>
Moreoever I would try to optimize the PME settings with the tools,<br>
g_tune_pme and g_pme_error, which give you performance and accuracy of<br>
the parameters, respectively.<br>
<br>
So perhaps with some more information I can provide more help.<br>
<br>
/Flo<br>
<br>
><br>
> Thanks!<br>
> Denzil Frost<br>
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</div>--<br>
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Dipl. - Phys.<br>
<br>
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University Stuttgart<br>
<br>
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