[gmx-users] how to fix atoms in bulk?

[Xavier Periole]

I guess it is water you want to fix ! I had to do that one and the 
way I turned around the problem was to define a new type of 
water with exactly the same definition as SPC except it was 
called EAU (water in French :)) ). After that all the water molecules
I wanted to be fix had there name changed to EAU and I define
position restrains on them. And you can release the restrains 
afterwards. 

Hope it helps,
XAvier