[gmx-users] energy between different groups

[Faezeh Pousaneh]

Hi,

I simulate liquid water 1397 molecules with specifying two groups with
index file; 1 molecule and rest of the molecules 1396. When I obtain
average LJ energy per molecule for whole system (with -nmol), I get  16
kJ/mol, but when I obtain it from interaction between groups,
 LJ-SR:group1-group2, I get 8  kJ/mol. A factor of 2 is missing. Can any
one who knows please explain me why?

thank you
Best regards