From: John Stone (
Date: Tue Apr 21 2015 - 15:32:33 CDT

  Have a look at the VMD-CPMD tutorials written by Axel Kohlmeyer,
they contain some great examples of how to draw arrows and other
geometry for whatever custom visualization purposes you have in mind:

Unfortunately, any scheme you might use to calculate
velocities "after the fact" is doomed to be incorrect, since
trajectories typically skip timesteps and subtracting positions
will not restore the correct velocity information. For this reason,
velocity informatino must normally be written to trajectory files
at simulation time.

  John Stone

On Tue, Apr 14, 2015 at 09:34:42PM +0330, Hojjat Behmadi wrote:
> Dear VMD users
> I am new to VMD and would like to simulate the problem of N spherical
> micro-particles in two dimensions. I have the coordinates of particles in
> an xyz-file and can visualize them with VMD. But two questions has been
> remained:
> 1- How can I put an arrow on each particle demonstrating it's direction of
> motion(e.g. for velocity field)?
> 2- Is there any approach to calculate each particle's velocity?
> Cheers,
> Hojjat Behmadi

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