[gmx-users] Problem with energy minimisations using TIP4P

[Ran Friedman]

Dear GMX users and developers,

I'm resending this message since I didn't get any answer and I'm afraid
my question wasn't clear enough.

Do you have any idea as for the source of my problems with the
minimisations using the TIP4P water model? Did anyone succeed in such
minimisations (using GMX 3.2.1) and can give me a hint?

Thank you,
Ran.

-------- Original Message --------
Subject: Energy minimisation with TIP4P
Date: Tue, 23 Mar 2004 11:29:27 +0200
From: Ran Friedman <ran at hemi.tau.ac.il>
To: gmx-users at gromacs.org

Dear GMX users and developers,

When trying to minimise a system which consists of a solute in a water
box, with the OPLS FF and TIP4P water, I end up with very large forces,
e.g. "Maximum force     =  3.0970608e+06 on atom 16811". I tried several
integrators, different solutes, etc. and I always get the same error.

When using TIP3P water, the energy is converged and the minimisation
succeeds.

I use Gromacs 3.2.1, and an octahedral box. I didn't change the default
density of the box. A sample .mdp file is attached.

I'd appreciate any comments.

Ran.

--
------------------------------------------------------
Ran Friedman
Laser laboratory for fast reactions in biology
Department of biochemistry
Faculty of life sciences
Tel-Aviv university
972-3-6409824
------------------------------------------------------
-------------- next part --------------
title		    =  EM of a small solute
cpp                 =  /lib/cpp
define              =  -DFLEXIBLE
constraints         =  none
integrator          =  l-bfgs
nbfgscorr           =  10
nsteps              =  10000
nstlist             =  10
ns_type             =  grid
rlist               =  1.2
coulombtype         =  PME
rcoulomb            =  1.0
vdwtype             =  Switch
rvdw                =  1.0
rvdw_switch         =  0.8
fourierspacing      =  0.10
fourier_nx          =  0
fourier_ny          =  0
fourier_nz          =  0
pme_order           =  4
ewald_rtol          =  1e-5
optimize_fft        =  yes
;
;	Energy Minimising stuff
;
emtol               =  100
emstep              =  0.02
;
;	Output
;
nstxout             =  10