[gmx-users] GROMACS 4.5.4 keep crashing all the time

[Tsjerk Wassenaar]

Hi Chris,

I can imagine that the pressure scaling has a more profound effect on
the 'visible' surroundings if a cut-off is used, while this will not
be the case when using PME. So the shock for an atom when the
coordinates are adjusted can be expected to be greater with cut-off
based methods, rendering such simulations less stable. As for SD,
probably that causes sufficient damping of jitter introduced due to
pressure coupling for it not to propagate and cause problems.
But those are just my two cents (about 2.8 dollar cents with current rates :p).

Cheers,

Tsjerk

On Thu, Sep 1, 2011 at 2:41 PM,  <chris.neale at utoronto.ca> wrote:
> I am glad that the pressure coupling intervals have been identified as a
> source of instability for poorly equilibrated systems as I was unaware of
> that. Still, the fact that the SD integrator also solves the problem also
> suggests that this is simply a poorly equilibrated system. I am not sure why
> PME would run fine and reaction field would give lincs warnings, but then
> again I have no experience with using a reaction field.
>
> Chris.
>
> On 1/09/2011 6:32 PM, Itamar Kass wrote:
>>
>> Hi Tsjerk,
>>
>> Thanks for the help, it actually worked. When nstpcouple is set to 1m the
>> system can be equilibrated (NPT) without LINCS error. I hadn't thought about
>> it as I never use NVT (unless doing FE calculations).
>
> Equilibrating with NVT before NPT can be wise when the system starts far
> from equilibrium.
>
>>
>>
>> Is this mean the 4.5.4 is more sensitive the 4.0.7? Is this effect the
>> data collected till now? If this is the case, why 5 ns simulations done with
>> 4.0.7 crashed when extended it using 4.5.4?
>
> IIRC 4.0.x and 4.5.x have different mechanisms for deciding how often to
> do global communication for things like T and P coupling. Mostly you can
> get away with the same kind of approximation one uses with twin-range
> neighbour lists, periodic neighbour list updates, RESPA, etc. where
> slowly-varying quantities don't have to be recalculated every step.
> However during equilibration (and that includes the transition from
> 4.0.x to 4.5.x) those assumptions need not be valid. So tuning the
> update frequency to be high during transitions is a good idea. Then
> relax them and see how you go.
>
> Mark
>
>>
>> Also, is this mean I can do my productive run using 4.5.4 with the default
>> value of nstpcouple, it seems that setting it to 1 greatly increases the
>> computational time. To the best of my knowledge, in prior version nstpcouple
>> was set to 1 by default.
>>
>> Cheers,
>> Itamar
>>
>>
>> On 01/09/2011, at 4:47 PM, Tsjerk Wassenaar wrote:
>>
>>> Hi Itamar,
>>>
>>> I haven't really followed the discussion and I'm a bit too lazy to
>>> look it all up now ;) But have you tried setting the nst parameters to
>>> 1  (except for output). Especially nstpcouple. Note that nstpcouple=1
>>> requires nstlist=1 and nstcalcenergy=1. If that solves the problem,
>>> you may need to extend your equilibration a bit, first relaxing NVT,
>>> followed by NPT with nstpcouple=1, thereafter equilibrating using
>>> productions conditions. It it solves it, maybe the option should be
>>> renamed nstptrouble :p
>>>
>>> Hope it helps,
>>>
>>> Tsjerk
>>>
>
>
>
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-- 
Tsjerk A. Wassenaar, Ph.D.

post-doctoral researcher
Molecular Dynamics Group
* Groningen Institute for Biomolecular Research and Biotechnology
* Zernike Institute for Advanced Materials
University of Groningen
The Netherlands