[gmx-users] How deuterium order parameters computed?

[Bin Liu]

Hi Everyone,

I have a question about the implementation details of g_order. When I was
reading literatures, I found several interpretations of how the deuterium
order parameters are computed. One is calculate S_{ij} first, then

S_{CD} = \frac{2}{3} S_{xx} + \frac{1}{3} S_{yy}.

Another approach is assuming ideal tetrahedral geometry of the C-D bonds
and the two neighbouring carbons, then reconstruct the coordinates of both
possible Ds, then take the average of the angles between the C-D bonds and
the system normal.

I am curious about that if they are equivalent and which approach was
implemented into GROMACS. It seems the cited paper in g_order.c didn't
mention either of them.

A new order parameter for tetrahedral configurations P.-L. CHAU and A. J.
HARDWICK  MOLECULAR PHYSICS, 1998, VOL. 93, NO. 3, 511- 518

Thanks for your clarification.

Bin