[gmx-users] Help regarding potential energy

[Gaurav Saraf IDD M Tech Biochem. Engg, IIT (BHU)]

Dear Gromacs users,
I am doing a protein-peptide simulation using gromos43a1 forcefield
(as per the tutorial)
When i do the energy minimization step before beginning equilibration,
I get the following results:

Steepest Descents converged to Fmax < 1000 in 652 steps
Potential Energy  = -8.04234816499126e+05
Maximum force     =  9.71976935137859e+02 on atom 4612
Norm of force     =  2.70955252439520e+01

But when I check with g_energy_d -f em.edr (and then 10 0 {for
potential}), I get

Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
Potential                1.36118e+09    1.3e+09 1.52478e+10
-7.91307e+09  (kJ/mol)

The potential is showing positive... what could be wrong?

Thanking you,
Regards,
Gaurav.
School of Biochemical engineering
IIT BHU, INDIA.