[gmx-users] problem with energy minimization

Bert de Groot bgroot at gwdg.de
Thu Dec 13 13:25:28 CET 2001

hugo verli wrote:

> I'm having the same problem that Geraudis mention. I did try the define sugested
> by David but I still have the following error:
> Step =   218, Dmax = 2.84e-05 nm, Epot = -2.74076e+05 Fmax = 5.35193e+02
> Step =   220, Dmax = 1.70e-05 nm, Epot = -2.74076e+05 Fmax = 5.09737e+02
> Step =   221, Dmax = 2.04e-05 nm, Epot = -2.74076e+05 Fmax = 4.78996e+02
> Step =   226, Dmax = 1.53e-06 nm, Epot = -2.74076e+05 Fmax = 4.76698e+02
> Stepsize too small Converged to machine precision,
> but not to the requested precision (100)

this is not an error. it just means that with your present parameters
you cannot minimize your energy further. And for 99% of all cases, like
e.g. starting an MD ismulation from the resulting structure, this should
already suffice. Only for special purposes (like for example a Normal Modes
type of calculation) you would need to minimize further, but then you
a) should not use a cut-off (because you get fluctuations in the energies
because of that and b) should probably move to double precision.


Dr. Bert de Groot

Max Planck Institute for Biophysical Chemistry
Theoretical molecular biophysics group
Am Fassberg 11 
37077 Goettingen, Germany

tel: +49-551-2011306, fax: +49-551-2011089

email: bgroot at gwdg.de

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