[gmx-developers] angle restraints

David Mobley dmobley at gmail.com
Fri Mar 24 14:59:09 CET 2006


> I think this case is not defined so uniquely.
> I assume you want to distinguish \| from /|.
> But is the angle \| equal to |/ (rotated system)?
> And \| with one vector moved through pbc is | \.
> So with the definition I assume you would like
> to have the angle depends on the distance between
> the vectors and the sign will change when the shortest
> distance between the vectors switches pbc.

Hmm. Good point. But, this is handled for g_angle, right? That is, I
can compute the (correct) angle between two vectors using g_angle. I
would like to then be able to fix that same angle using simple
harmonic restraints. Unfortunately, it isn't now possible to do so; I
have to use this cosine functional form. It seems to me if I can
measure it, I should also be able to fix the value... Unless the same
problem applies to how it's measured? (If so, this should probably be
pointed out in the docs). I am not sure I've checked that the angles
computed with g_angle lie on 0 to 360 (or -180 to 180) rather than 0
to 180 as would happen if these cases aren't distinguished.

If you still think this is a problem, I'm open to any suggestions on
how I can make the angle I'm interested in rotate through 360^o
without getting stuck at the alternate zero of the force...


> Berk.
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