[gmx-users] Coul-SR: positive value for interating group

[Raj D]

Dear Users,
I have just completed simulation of a ligand and enzyme complex and
when I visualized the  trajectory , I have noted an important close
contact say about (7 to 10 A distances) between an active site residue
Arg and the carboxylate group of the ligand through out the simulation
time of 10ns. I wanted to quantify it using mdrun -rerun option and
evaluated energy (COUL-SR) value of the polor atoms of the Arg and
carboxylate as energygroup in my mdp file , and surprisingly I found
the values are big positive numbers whereas I expected a negative
values. Why the contradiction happens , trajectory showed attraction
and energy is dispersion ?

I just pasted few lines of the energy.xvg
@ s0 legend "Coul-SR:Arg262_NH-CPG_COOH"
@ s1 legend "Coul-14:Arg262_NH-CPG_COOH"
    0.000000    5.647315    0.000000
    2.000000    5.367461    0.000000
    4.000000    6.109462    0.000000
    6.000000    0.976809    0.000000
    8.000000    4.306820    0.000000
   10.000000    2.926659    0.000000
   12.000000    2.567632    0.000000
   14.000000    1.934579    0.000000
   16.000000    3.874691    0.000000
   18.000000    3.130555    0.000000
   20.000000    1.804790    0.000000

expecting you experts opinion on this.

Regards,
Raja