[gmx-users] Drift with groups+tabulated potential.

[sperez14 at us.es]

Dear GROMACS Community, 

I am trying to do a simulation using a tabulated potential which forces
me to use the group cut-off. I get a drift in the conserved quantity of
-600KJ/mol/ns. My system consists of 1000 rigid TIP4P water molecules
and a Na+ ion. It seems that the problem is in the group cut-off since
when I change the tabulated potential for a regular vdw the problem
persists. I have followed the instructions of:  

 http://www.gromacs.org/@api/deki/files/94/=gromacs_nb.pdf 

Is this the kind of energy drift acceptable? I include a copy of the
.mdp file. 

Thanks for your help, 

Sergio  

integrator = md 
dt = 0.001 
nsteps = 100000 
init-step = 0   
cutoff-scheme = group  
nst-list = 1  
verlet-buffer-tolerance = 0.0005 
ns-type = grid 
rlist = 1.3 
pbc = xyz 
coulombtype = PME-switch  
rcoulomb = 1.  
rcoulomb-switch = 0.95  
pme-order =  4 
fourierspacing =  0.1 
ewald-rtol = 1.e-5  
vdwtype = user   
rvdw = 1.0  
DispCorr = No 
tcoupl = v-rescale 
tc-grps = System 
;nsttcouple = 1 
tau-t = ref-t = 300.0  
constraints = all-angles 
constraint-algorithm = LINCS 
lincs_iter                  = 1  
lincs_order                 = 4  
energygrps = NA OW 
energygrp_table = NA OW 
comm-mode = linear