[gmx-users] Force constant for position restraints

[Mark Abraham]

On 8/05/2010 8:30 PM, shahab shariati wrote:
> Hi gromacs users
> there is a option in pdb2gmx command : -posrefc (Force constant for
> position restraints).
> and also there is following lines in top file:
> #ifdef POSRES
> #include "posre.itp"
> #endif
> which of them is better way for position restraint simulation and
> determining of force constant?
> Any help will highly appreciated!

They work together. If your .mdp uses "define = -DPOSRES" then that .itp 
file is used. See, for example, manual 5.7.3. The force constants in 
that .itp file are the value of -posrefc. The value of those force 
constants is largely irrelevant for normal purposes of preparing 
structures for MD.

Mark