<div dir='auto'>Hi,<div dir="auto"><br></div><div dir="auto">We don't have such functionality planned.</div><div dir="auto">But velocities are extremely correlated over several time steps. You should be able to write output every 10 steps without significantly reducing the statistics.</div><div dir="auto">Alternatively, if you are running in without domain decomposition, you can quickly hack a printf statement in the code.</div><div dir="auto"><br></div><div dir="auto">Cheers,</div><div dir="auto"><br></div><div dir="auto">Berk</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Oct 9, 2018 17:48, Andreas Baer <email@example.com> wrote:<br type="attribution" /><blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>
Dear developers,<br />
within my simulations, I encounter the problem, that I have to save
the forces and velocities of the whole system, even though I need
only those for very few atoms (in my case: a small particle e.g. a
fullerene, further details: see below). This generates a lot of
unnecessary data and also slows down the simulation a lot, as I have
to write out the trajectory every step (2 fs).
A possible solution would be to write forces and velocities only for
a group of atoms, as is possible for the compressed trajectory for
positions (.xtc). So far, I did not find any possibility doing that
and also no upcoming features.
Did I miss anything? If no, is this, or a similar functionality
planned for a future release?
If neither of this, is there a chance to do it myself, ether only
for my personnel use or as an official contribution?
Some further details to my simulation:
A nanosized particle (artificial or fullerene) is dissolved in a box
of solvent (10<sup><span style="display:inline-block;width:0;height:0">^</span>5</sup>
to 10<sup><span style="display:inline-block;width:0;height:0">^</span>6</sup>
molecules). Transport coefficients should be calculated using the
Green-Kubo formalism. Thus, velocities and forces are required at a
very high frequency, so that I write out every step. As I only need
the information for the particle, I get a huge amount of unused
data, that I have to postprocess, to retrieve the desired
information. The biggest problem is, that this slows down my
simulation by a factor of roughly 20, depending on the hardware