[gmx-users] problems with energy minimization

Martin mstiebri at biologie.uni-erlangen.de
Mon Aug 28 14:21:48 CEST 2006

Dear all,

I´m a beginner in the field of molecular dynamics and have just installed the 
gromacs software.
I have problems with energy minimization. When trying out the md tutorial on 
the lysozyme structure 1AKI.pdb using the provided minim.mdp file the 
minimization finishes with the message:

  Stepsize too small, or no change in energy.
  Converged to machine precision,
  but not to the requested precision Fmax < 1000
  You might need to increase your constraint accuracy, or turn
  off constraints alltogether (set constraints = none in mdp file)

  writing lowest energy coordinates.

  Back Off! I just backed up minim_traj.trr to ./#minim_traj.trr.4#

  Back Off! I just backed up confout.gro to ./#confout.gro.4#

  Steepest Descents converged to machine precision in 79 steps,
  but did not reach the requested Fmax < 1000.
  Potential Energy  = -1.13948846313191e+04
  Maximum force     =  1.94715000386709e+03 on atom 1113
  Norm of force     =  8.53155624640669e+03

I already tried different minimization algorithms with different settings and 
also compiled the code with double precision accuracy without success.

Thank you very much for any advice,

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