[gmx-users] g_sas : Total surface area

[Kavyashree M]

Dear users,

I was calculating solvent accessible surface area for a trajectory
using g_sas. I used an index file with 3 sets (A, B, C) of mutually
exclusive residues but summing up to 20 amino acids. Then using
g_sas calculated sas for these 3 sets separately and whole protein
separately for the same trajectory.
I was expecting that the average value of
Total surface area (protein) ~ Total surface area (A)+Total surface area
(B)+Total surface area (C)
But it is not so.
Could anyone explain me why?

Thank you
Kavya