[gmx-users] step size too small

minnale minnale_gnos at rediffmail.com
Mon Jun 30 11:26:46 CEST 2008

Hi all, 
     1) I have embedded protein into popcbilayer
2) Energy minimisation 
3) Later added ions by using genion, 
4) When I am trying to run minimisation its showing following sentences

 Stepsize too small, or no change in energy.
Converged to machine precision,
but not to the requested precision Fmax < 100

Double precision normally gives you higher accuracy.
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 converged to machine precision in 49 steps,
but did not reach the requested Fmax < 100.
Potential Energy  = -2.1825061e+05
Maximum force     =  4.3672461e+03 on atom 7008
Norm of force     =  5.5597691e+04

my .mdp file is
cpp                 = /usr/bin/cpp
define              =  -DFLEX_SPC
constraints         =  none
integrator          =  steep
nsteps              =  500
;       Energy minimizing stuff
emtol               =  100
emstep              =  0.01
nstcomm             =  1.0
ns_type             =  grid
rlist               =  1.0
rcoulomb            =  1.0
rvdw                =  1.0

When I run minimisation before adding ions it ran fine but later not why?
I have searched about solve this problem in archives list and I understood that this not an error. Can I proceed further simulations
Any comments will be appreciated. 

Thanks in advance.

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