[gmx-users] warter freeze into ice when "cutoff-scheme=Verlet" and "coulombtype = cut-off "

[niexuechuan]

Hi everyone,
         I found that after gromacs version 4.6, when set "cutoff-scheme=Verlet" and "coulombtype= cut-off", the waters in the system will freeze into ice.  I known that charge-groups are necessary when using plain cut-off electrostatics. But I'm surprised that why the waters freeze into ice when using plain cut-off electrostatics without charge-groups?  Could someone explain how it happenes?


My mdp files are like this:


integrator               = md
constraints              = all_bonds
dt                       = 0.002
nsteps                   = 50000000
comm-mode               =None 
nstxout                  = 0
nstvout                  = 0
nstfout                  = 0
nstlog                   = 25000
nstxtcout                = 500
xtc-precision            = 1000
energygrps               = MOL  SOL
nstlist                  = 1
ns_type                  = grid
pbc                      = xyz
rlist                    = 1.0
coulombtype              = cut-off 
rcoulomb-switch          = 0
rcoulomb                 = 1.0
vdw-type                 = cut-off 
rvdw-switch              = 0
rvdw                     = 1.0
Tcoupl                   = V-rescale
nsttcouple               = -1
tc-grps                  = MOL    SOL    
tau_t                    = 0.1    0.1   
ref_t                    = 300  300       
freezegrps               = MOL
freezedim                = Y Y Y  
   
Thanks!
Xuechuan