[gmx-users] temperature too high with reaction field

[Berk Hess]

Hi,

This is normal.
Reaction-field still uses a cut-off, which gives cut-off errors.
To make the the error small you will need to reduce tau_t.
Or use reaction-field-zero with a buffer region (computationally expensive).
The real solution is to simply use PME.

Berk

> Date: Wed, 21 Jan 2009 17:51:02 +0100
> From: sam.moors at chem.kuleuven.be
> To: gmx-users at gromacs.org
> Subject: [gmx-users] temperature too high with reaction field
> 
> Hi gmx users,
> 
> I'm trying to simulate a water box filled with TIP3P water.
> With PME, everything seems OK.
> However, when I switch to reaction field electrostatics,
> the temperature in the output files is too high: 
> 312K instead of 300K (the t_ref value for the whole system).
> Maybe there is something wrong with my input paramters?
> Below you find my .mdp file
> 
> Thanks,
> Sam
> 
> integrator  = md
> dt   = 0.002 ; ps !
> nsteps   = 20000
> nstcomm  = 1
> nstxout  = 500
> nstvout  = 0
> nstlog  = 500
> nstenergy = 500
> nstfout  = 0
> nstlist  = 10
> ns_type  = grid
> rlist   = 1.2
> coulombtype  = Reaction-Field 
> epsilon_r = 1
> epsilon_rf = 78
> rcoulomb  = 1.2
> table-extension = 1
> vdwtype  = cutoff
> rvdw   = 1.2
> fourierspacing  = 0.19
> fourier_nx  = 0
> fourier_ny  = 0
> fourier_nz  = 0
> pme_order  = 4
> ewald_rtol  = 1e-5
> optimize_fft  = yes
> ; temperature coupling
> Tcoupl   = v-rescale
> tau_t   = 1.0
> tcgrps   = system
> ref_t   = 300
> ; Pressure coupling
> Pcoupl = parrinello-rahman
> tau_p = 1.0
> compressibility = 4.5e-5
> ref_p = 1.0
> ; Generate velocites
> gen_vel  = no
> gen_temp  = 300
> gen_seed = 173529
> 
> 
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