[gmx-users] Question about 'mdrun -nosum'

[Mark Abraham]

On Fri, Dec 14, 2012 at 3:46 PM, Thomas Schlesier <schlesi at uni-mainz.de>wrote:

> Dear all,
> i have a small question regarding the '-nosum' option of 'mdrun'.
> The manual states:
>
> For a global thermostat and/or barostat the temperature and/or pressure
> will also only be updated every nstlist steps. With this option the energy
> file will not contain averages and fluctuations over all integration steps.
>
> Second sentence is clear to me. But the first sentence give me some
> thoughts.
> I think this would introduce some errors, but what is about the magnitude
> of these?
>

Indeed, that does introduce a new approximation, but as you and Dawei said
it's probably drowned out in the noise. Constant point charges are not a
very good model for much...

There is work going on to try to make it easier to quantify these kinds of
(non-)effects, e.g. http://arxiv.org/abs/1208.0910

Mark

I would expected that the errors are in the same order of the errors in the
> forces due to the neighborlist search (error due to the fact that one uses
> 'nstlist=5' instead of 'nstlist=1') and would be more or less negilegible,
> if one doesn't use a very larger 'nstlist'-value.
>
> But to be on the save side i wanted to ask.
>
> Greetings
> Thomas
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