R: RE: R: RE: R: RE: [gmx-users] Tabulated potential - Problem

[albitauro at virgilio.it]

In my simulation I used bond type 9 because I was convinced that 1-2 LJ interaction would have been excluded  in any case as default for bond stretching interaction. After my simulations it seems not and so I suppose that I must use bond type 8 and list the exclusion in the itp...Right?

Alberto  

----Messaggio originale----
Da: gmx3 at hotmail.com
Data: 29-set-2009 2.15 PM
A: "Discussion list for GROMACS users"<gmx-users at gromacs.org>
Ogg: RE: R: RE: R: RE: [gmx-users] Tabulated potential - Problem


-->Are you really sure about this and that this is with bond type 8?

The whole point of having a tabulated bond type 8 and 9
is that 8 does generate exclusions and 9 does not.

Berk



Date: Tue, 29 Sep 2009 14:17:37 +0200
From: albitauro at virgilio.it
To: gmx-users at gromacs.org
Subject: R: RE: R: RE: [gmx-users] Tabulated potential - Problem

Hi,

in order to check further which kind of problems are present when using
tabulated potential, I carried out two simulations on the same system by using the same harmonic
potential for bond stretching but either in analytical form or in tabulated form respectively. The
results of the two simulations are different!
I repeated the calculationis on just two bonded particles and I verified that when using
analytical stretching potentials 1-2 LJ interactions are excluded while they
are not excluded when using tabulated potential.
Am I right?

This should mean that I have to use a function type 8 and list explicitly the elements of the [
exclusions ] field or is there another method?

Thanks

Alberto

----Messaggio originale----
Da: gmx3 at hotmail.com
Data: 25-set-2009 12.27 PM
A: "Discussion list for GROMACS users"<gmx-users at gromacs.org>
Ogg: RE: R: RE: [gmx-users] Tabulated potential - Problem

Your system could be unstable.
You can check for large forces with mdrun -pforce
I don't know what a reasonable range of forces is, you can try 5000.
If you have instabilities, you should get large forces printed
before you get the fatal error.

Berk




Date: Fri, 25 Sep 2009 14:10:08 +0200
From: albitauro at virgilio.it
To: gmx-users at gromacs.org
Subject: R: RE: [gmx-users] Tabulated potential - Problem

Unfortunately, my box sizes are not close to 23. I also carried out calculations switching off PBC or on much smaller systems. 
I received always the same error. 
I tried also a geometry optimization. It finished without warnings nor errors: anyway the potential energy changed only very slightly during the simulation with too large values.

Thanks

AM

----Messaggio originale----
Da: gmx3 at hotmail.com
Data: 24-set-2009 11.29 AM
A: "Discussion list for GROMACS users"<gmx-users at gromacs.org>
Ogg: RE: [gmx-users] Tabulated potential - Problem

This is not nonsense, it is exactly what is says.
The distance between two atoms is more than 10 times as large as your table length.

Maybe you are somehow having issues with periodic boundary conditions.
Is you box size close to 23?

Berk




Date: Thu, 24 Sep 2009 12:32:36 +0200
From: albitauro at virgilio.it
To: gmx-users at gromacs.org
Subject: [gmx-users] Tabulated potential - Problem

Hi,

I'm trying to carry out a CG simulation and I'm using
a tabulated potential for a bond stretching term.
My MD simulations stops immediately with the error message:

-------------------------------------------------------
Program mdrun_mpi, VERSION 4.0.5
Source code file: bondfree.c, line: 1772

Fatal error:
A tabulated bond interaction table number 0 is out of the table range: r 23.678833, between table indices 12069 and 12070, table length 1020
-------------------------------------------------------

This should mean that some distances are beyond table length (as reported in the manual) but this is
nonsense considering my input files and topology.

Do you have any suggestion?
Thanks!

AM




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