[gmx-users] Steepest descent

[David van der Spoel]

On Fri, 30 Nov 2001, Andrew Horsfield wrote:

>  Step =     0, Dmax = 1.00e-02 nm, Epot = -8.68044e+03 Fmax = 1.82046e+04
>  Step =     1, Dmax = 1.00e-02 nm, Epot = -1.00319e+04 Fmax = 6.48675e+03
>  Step =     2, Dmax = 1.20e-02 nm, Epot = -1.16666e+04 Fmax = 3.59934e+03
>  Step =     3, Dmax = 1.44e-02 nm, Epot = -1.28017e+04 Fmax = 1.99101e+03
>  Step =     4, Dmax = 1.73e-02 nm, Epot = -1.36208e+04 Fmax = 1.65291e+03
>  Step =     5, Dmax = 2.07e-02 nm, Epot = -1.38893e+04 Fmax = 1.57456e+03
>  Step =     8, Dmax = 6.22e-03 nm, Epot = -1.38896e+04 Fmax = 1.56714e+03
>  Step =    21, Dmax = 1.82e-06 nm, Epot = -1.38896e+04 Fmax = 1.63983e+03
>  Stepsize too small Converged to machine precision,
>  but not to the requested precision (500)
>  You might need to increase your constraint accuracy
>
>I have tried turning off constraints, using double precision binaries,
>conjugate gradient, PME and cut-off for the electrostatics, but the result
>is always the same. What else can I try to fix this?
If you get this very message, it means you still have contstrains left:
check the value for constraints in your .mdp file (should be none) and you
topology (do you have flexspc.itp instead of spc.itp?)

You can check your tpr file with
gmxdump -s topol.tpr | more
and then search for SETTLE (water) or SHAKE (other constraints)

Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel
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