[ESPResSo-users] have_quaternion

[Martin Kaiser]

Dear all,

I have an issue regarding the have_quaternion option for the virtual sites 
implementation. My setup looks as follows:

I have two particles, one of them is a Langevin swimmer, the second is a 
dipole. The dipole is a virtual site to the swimmer. My goal is to let the 
dipole and the propulsion force always show into the same direction. This means 
for me, that the director of both particles should show into the same 
direction. The have_quaternion option should, to my understanding, update the 
orientation of the virtual particle so it always has the same orientation 
compared to the orientation of the real particle.

Unfortunately, as soon as I activate the have_quaternion feature, the director 
of my virtual particle is set to [0,0,0]. I have no idea why that happens and, 
in case it is intended, what it means.

So the issues are:
- Fix the orientation of directors of real and virtual, relative to each other.
- have_quaternion sets virtual director to [000].

Thanks for the help!
Best,
Martin