[gmx-users] energy minimization

[Dhrubajyoti Maji]

Dear gromacs users,
 I am doing energy minimization of a neat urea system. When I set emtol =
10 the following result is obtained  :
Steepest Descents converged to machine precision in 33995 steps,
but did not reach the requested Fmax < 10.
Potential Energy  =  6.7910172e+04
Maximum force     =  7.8070724e+01 on atom 353
Norm of force     =  3.1714432e+00
and average energy is
Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
Potential                   72421.6       2500    14229.1   -16147.4
 (kJ/mol)
And when I set emtol=100 the following result is obtained :
Steepest Descents converged to Fmax < 100 in 12573 steps
Potential Energy  =  7.1502609e+04
Maximum force     =  8.5925835e+01 on atom 2713
Norm of force     =  5.0333209e+00
and average energy is
Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
Potential                   77654.4       3600    22408.3   -22901.6
 (kJ/mol)
In both cases the energy is well converged but not less than zero. Does
only convergence of potential energy (not negative) guarantee the
completion of EM process ? If so then what emtol value should  I use ?
Any help will be highly appreciated. Thanks for your time.
Best regards
Dhrubajyoti Maji