[gmx-users] About rlist, rvdw

[高恺]

Dear gromacs users,

I have recently done some simulations of CH4-Graphite desorption. I put methane into the graphite pores, and the pores are connected to the outside by a channel, allowing methane to spontaneously desorb because of the pressure difference and finally reach equilibrium.
This is a simple simulation, but I noticed that using different rlist, rvdw values, the density of methane in the hole will be significantly different after the system is equilibrated.
In my understanding, the larger the rlist/rvdw, the closer the simulation results are to the real world. But I don't understand why rlist/rvdw has such a big impact on simulation results. If the result of setting rlist=2 is significantly different from the result of setting rlist=1, does it mean that the result of setting rlist to 1 is not trusted? 

I am using following parameters (mdp file):
------------------------------------------------------
; Run parameters
integrator                   = md
nsteps                        = 20000000
dt                               = 0.001
comm-mode              = None

; Output control
nstxout                  = 50000
nstvout                  = 50000
nstfout                   = 50000
nstlog                    = 50000
nstenergy               = 50000
nstxtcout                = 1000
xtc_precision           = 10000
energygrps             = GRA GAS

; Neighborsearching
ns_type                  = grid
nstlist                     = 5
rlist                         = 1

; VDW
vdw-type                 = cut-off
rvdw                         = 1

; OPTIONS FOR ELECTROSTATICS 
coulombtype              =cut-off    
rcoulomb                    = 1

; Periodic boundary conditions
pbc                             = xyz

; TEMPERATURE COUPLING
Tcoupl                   = nose-hoover
tc_grps                  = GRA GAS
tau_t                      = 2 2
ref_t                       = 400 400

; VELOCITIES GENERATION
gen_vel                     = yes
gen_temp                 = 400
gen_seed                  = 391482

; ENERGY GROUP EXCLUSIONS
energygrp_excl           = GRA GRA

; Other Settings
freezegrps               = GRA
freezedim                = Y Y Y
-------------------------------------------------------------------

I would be very grateful if anyone can help me.

Kevin