[gmx-users] POSRES for umbrella sampling

[stellatof]

Dear all,
I have a question regarding the use of "POSRES" in .
In the umbrella sampling tutorial it says that POSRES is used to keep 
one chain as an immobile reference in the pulling procedure. What is the 
effect of POSRES? Does it keep the molecule center of mass fix or does 
it restrain the positions of atoms inside the molecules? According to 
the manual I tought the latter one, but then I don't understand how this 
helps in having an immobile reference.
What problem would one have if not using the POSRES?

In the simulations I performed, when I pull one molecule, the one I 
restrained using POSRES keeps its center of mass stable and has only 
small changes in its internal structure. Is it the expected behaviour?

Thanks in advance and best regards,

Francesco


-- 
Francesco Stellato, PhD
I.N.F.N. - Rome 'Tor Vergata'
Tel: +39 06 7259 4284