[gmx-users] Minimization stops without reaching the requested precision Fmax < 1000

[Dallas Warren]

Already replied
https://mailman-1.sys.kth.se/pipermail/gromacs.org_gmx-users/2019-June/125707.html

Which just links to
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
which explains what the error message means.

Catch ya,

Dr. Dallas Warren
Drug Delivery, Disposition and Dynamics
Monash Institute of Pharmaceutical Sciences, Monash University
381 Royal Parade, Parkville VIC 3052
dallas.warren at monash.edu
---------------------------------
When the only tool you own is a hammer, every problem begins to resemble a nail.

On Tue, 25 Jun 2019 at 19:51, Mahdi Bagherpoor <mehdi.bpour at gmail.com> wrote:
>
> Dear Gromacs Users,
>
> I am trying to add the tetrahedral zinc atom dummy model into CHARMM36
> force field in Gromacs. In my system, this dummy zinc interact with four
> Cystein residues (CYM).  The parameters of the zinc are available in CHARMM
> format, which I used to use it in NAMD package. After adding appropriate
> parameters, when I do energy minimization, I get this error:
> ========================
>
> Energy minimization has stopped, but the forces have not converged to the
> requested precision Fmax < 1000 (which may not be possible for your system).
> ...
> Steepest Descents converged to machine precision in 1045 steps,
> but did not reach the requested Fmax < 1000.
> Potential Energy  = -1.5922652e+06
> Maximum force     =  3.2106902e+07 on atom 3526
> Norm of force     =  1.4857810e+05
>
> ============================
> Atom 3526 is dummy atom of zinc ion. The dummy parameters added in
> ffbonded.itp file are:
> ---------- ffbonded.itp
>
> ;zinc dummy model, bonds
>       HK       ZD     1   0.09000000    451872.00
>       HK       HK     1   0.14700000    451872.00
> ;zinc dummy model, angles
>       HK       ZD       HK     5   109.500000   460.240000   0.00000000
>     0.00
>       HK       HK       HK     5    60.000000   460.240000   0.00000000
>     0.00
>       HK       HK       ZD     5    35.250000   460.240000   0.00000000
>     0.00
> ;zinc dummy model, dihedrals
>       ZD       HK       HK       HK     9    35.300000     0.000000     2
>       HK       ZD       HK       HK     9   120.000000     0.000000     2
>       HK       HK       HK       HK     9    70.000000     0.000000     2
>
> ----------- ffnonbonded.itp
>
> ;zinc dummy model
>    ZD    30    61.380000    0.000  A  0.310000000000  0.00001
>    HK     1     1.008000    0.500  A  0.000000000000  0.00000
>
> =================================================
> In contrast to Gromacs, when I do minimization in NAMD, there is no such an
> error in minimization. I should mention that I am using single precision
> platform of Gromacs.
> I would appreciate if you could share me in case you have some ideas about
> this problem.
>
> Cheers,
> Mahdi
> --
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