[gmx-users] stepsize too small

[Per Larsson]

Hello!

There are many discussions on the maillist about this...

In short, if all you want to do is normal md, it should be ok to just  
proceed with that. Just check that your potential energy is negative  
and everything should fine.

Otherwise, recompiling Gromacs to use double precision might get you  
a bit lower in energy, or change integrator to see if you get any lower.

Cheers
/Per


13 aug 2007 kl. 20.08 skrev burkhard rammner:

>
> Hi,
>
> This is the first time I`m using gromacs.
> That`s why I`m having a beginners`question.
> I tried to do an energy minimization, but after 45 steps this  
> message appears
> and I know that the following lines have led to questions before:
>
> "Stepsize too small (9.09769e-007 nm)Converged to machine precision,
> but not to the requested precision (1000)"
>
> I`m using single precision windows compiled gromacs. I know, I have
> to change whatever parameter, but so far I didn`t succeed.
>
> This is the mdp file:
>
> integrator        = steep           emtol              =  
> 1000           emstep           = 0.01
> nsteps            = 200           nstenergy       =  
> 10               nstxtcout        = 10                
> xtc_grps        = Protein           energygrps     =  
> Protein           nstlist             = 5           ns_type          
> = simple       rlist               = 1.0                
> coulombtype    = cut-off           rcoulomb      =  
> 1.0               rvdw            = 1.0                
> constraints    = none           pbc              = no
> So, what`s wrong here?
> What do I have to change?
>
> Many thanks for help!
>
> Burkhard
>
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