[gmx-users] Order parameter

[sujithkakkat .]

Dear all,

     I am using GROMACS-4.6.5 for studying gas hydrates and related
systems.
A useful order parameter which indicates water to hydrate transition is the
F4 order parameter where F4 is related to the H--O--O--H dihedral angle for
a pair of water molecules.

   It is found that F4 parameter is very frequently mentioned in several
works on gas hydrates done using GROMACS.  I want to know whether GROMACS
can calculate the value of the F4 parameter. Or is it possible for the user
to define an order parameter?

The g_hydorder tool in GROMACS refers to an order parameter different in
definition from the F4 parameter.  (P.-L. Chau and A.J. Hardwick, Mol.
Phys., 93, (1998), 511-518.)

Please comment.

Regards,
Sujith.