[gmx-users] simple question about umbrella pulling

[Scott Milner]

Folks -- Reading Section 7.3.21 "COM pulling" in the GROMACS 4.0  
manual, I don't quite see how to specify a nonzero minimum distance  
for an umbrella potential.  I see that
	pull = umbrella
	pullgroup0 = ...
	pullgroup1 = ...
	pull_k1 = ... ; sets the force constant

but I don't see how to set "r0", for an umbrella potential between  
group0 and group1 of k1(r-r0)^2.  Surely this is possible?

Scott Milner
William H. Joyce Professor
The Pennsylvania State University
Department of Chemical Engineering
120 Fenske Laboratory
University Park, PA 16802
(814) 863-9355
smilner at engr.psu.edu