[gmx-users] problem in energy minimization

[Dallas Warren]

http://www.gromacs.org/Documentation/Errors#Stepsize_too_small.2c_or_no_change_in_energy._Converged_to_machine_precision.2c_but_not_to_the_requested_precision

On Tue, 17 Jul. 2018, 11:12 pm neelam wafa, <neelam.wafa at gmail.com> wrote:

> Hi,
>
> Dear gromacs users, I am running md simmulation of a protein with a ligand.
> i have already done it with the same protein and a different ligand. Now
> when i run em md run i get following result.
>
> Energy minimization has stopped, but the forces have not converged to the
> requested precision Fmax < 1000 (which may not be possible for your
> system).
> It stopped because the algorithm tried to make a new step whose size was
> too
> small, or there was no change in the energy since last step. Either way, we
> regard the minimization as converged to within the available machine
> precision, given your starting configuration and EM parameters.
>
> Double precision normally gives you higher accuracy, but this is often not
> needed for preparing to run molecular dynamics.
> You might need to increase your constraint accuracy, or turn
> off constraints altogether (set constraints = none in mdp file)
>
> writing lowest energy coordinates.
>
> Steepest Descents converged to machine precision in 150 steps,
> but did not reach the requested Fmax < 1000.
> Potential Energy  = -9.3659806e+05
> Maximum force     =  1.0269271e+04 on atom 4399
> Norm of force     =  9.8929054e+01
>
> NOTE: 10 % of the run time was spent in pair search,
>       you might want to increase nstlist (this has no effect on accuracy)
>  please guide me is it reliable to proceede for simmulation. or there is
> something wrong. Is it a sign of system instability?
>
> looking forward for your cooperation.
>
> Regards
> --
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