[gmx-users] oriientation angle of protein at interface

[mahreen arooj]

Hi All,
               I want to calculate orientation angle of protein at
organic/water interface as done in the following paper:” Replica-Exchange
Molecular Dynamics Simulation of Basic Fibroblast Growth Factor Adsorption
on Hydroxyapatite”

http://pubs.acs.org/doi/abs/10.1021/jp501463r



But, I don’t know how to define interface vector as the molecules at the
interface are periodic.



Can you please guide me in this regard



Thanks



Mahreen