[gmx-users] Energy minimisation with TIP4P

[Ran Friedman]

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
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-------------- 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