[gmx-users] oriientation angle of protein at interface

[mahreen arooj]

 Hi All,
              I want to calculate orientation angle of protein at organic/water interface asdone in the following paper:” Replica-ExchangeMolecular Dynamics Simulation of Basic Fibroblast Growth Factor Adsorption onHydroxyapatite”


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


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


 
Can you please guide me inthis regard


 
Thanks


 
Mahreen