[gmx-users] Implementing Radial Distance Constraints

Bob Johnson robertjo at physics.upenn.edu
Mon Apr 17 18:03:09 CEST 2006

Hello everyone,
My system consists of a carbon nanotube and various chemicals that adsorb to the
tube. I would like to use radial distance constraints to enforce adsorbates to
maintain a fixed distance away from the nanotube. These restraints must obey
the relation R = sqrt (x^2 + y^2) = user defined constant. With this type of
restraint the adsorbates are free to move along the z and circumferential
directions (something that can not be done with normal position or distance

I would like to add a restraint potential given by V = 1/2*k*(R-R0)^2 = 1/2*k*(
sqrt(x^2+y^2) - R0)^2. Here R0 is the fixed radial distance. Is this difficult
to implement in Gromacs? What file in the source code would I edit?
Bob Johnson

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