[gmx-users] Steepest Descents did not converge

Derrick Guang Yuh Lee k24dgyl at morgan.ucs.mun.ca
Wed Jul 9 18:24:01 CEST 2003

dear gmx-users

right now i am running the mdrun program in gromacs on a dppc lipid
bilayer (downloaded from the tieleman's website), and i keep on getting
this error:

Steepest Descents:
   Tolerance         =  1.00000e+02
   Number of steps   =      1000000
Step=  0, Dmax= 1.0e-02 nm, Epot= -2.99255e+05 Fmax= 5.37264e+03, atom=3275
Step=  1, Dmax= 1.0e-02 nm, Epot= -3.02471e+05 Fmax= 2.40785e+03, atom=3024
Step=  4, Dmax= 3.0e-03 nm, Epot= -3.02866e+05 Fmax= 1.90722e+03, atom=13315
Step= 16, Dmax= 1.8e-06 nm, Epot= -3.02866e+05 Fmax= 2.63245e+03, atom=16161

Stepsize too small (8.78906e-07 nm)Converged to machine precision,
but not to the requested precision (100)
You might need to increase your constraint accuracy, or turn
off constraints alltogether (set constraints = none in mdp file)

writing lowest energy coordinates.

Steepest Descents did not converge in 17 steps
  Potential Energy  = -3.02866e+05
Maximum force:  1.90722e+03

i've tried editing the constraints value to 'none' or changing it to
'all-bonds', and i've changed the value of emstep, but the only way i can
get the steepest decents to converge is by making the emtol value 
extremely high (emtol = 100000). any help would be appreciated.

 - derrick

 derrick Lee
 faculty of Science
 Memorial University of Newfoundland
 k24dgyl at mun.ca or derrickglee at hotmail.com
"a teacher is never a giver of truth - he is a guide, a pointer to the
truth that each student must find for himself. a good teacher is merely a
                                                              - bruce lee

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