[gmx-users] vdwtype = cut-off

[Mark Abraham]

On 11/10/11, Carla Jamous  <carlajamous at gmail.com> wrote:
> Hi everyone,
> 
> I ran my simulations with these parameters:
> 
> nstlist             =  10
> ns_type             =  grid
> rlist               =  0.9
> coulombtype         =  PME
> rcoulomb            =  0.9
> vdwtype             =  cut-off
> 
> rvdw                =  1.2
> 
> Apparently, in Gromacs, when using vdwtype =  cut-off, 
> 
> 
> 	
> 	
> 	
> 	pre.cjk { font-family: "DejaVu Sans",monospace; }p { margin-bottom: 0.21cm; }the potential changes discontinuously.
> 

The potential as a function of distance between any pair of atoms is discontinuous at the cutoff.


>  However, I have a constant LJ(SR) energy and a constant LJ(LR) energy, 
> 

So your particle density is nearly constant. Particles moving inside the cutoff balance those moving outside the cutoff. A changing value should indicate lack of equilibrium, not whether the cut-off is a significant source of error.


> although I didn't use either Switch or Shift. Please can anyone explain how does the cut-off really works in Gromacs and whether my simulations are correct or not?
> 

Please see the discussions in the manual for theory. Probably the simulations are fine.

Mark

> 
> 
> 
> Thanks
> 
> Carla
> 
> 
> 
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