[gmx-users] F4-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

Exact expression for F4 can be found in Phys. Chem. Chem. Phys., 2015, 17,
9509-9518.

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.)

It is found that F4 parameter is very frequently used in several works on
gas hydrates done using GROMACS (including the PCCP article mentioned
above). I was wondering whether it is possible for any version of GROMACS
to compute the value of F4 for my system (water + gas molecules). If not I
guess I would have to write a program to do the same.

Please comment.

Regards,

Sujith.