[gmx-users] problem with energy minimization

[Bert de Groot]

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.



Bert

____________________________________________________________________________
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
http://www.mpibpc.gwdg.de/abteilungen/071/bgroot
____________________________________________________________________________