[gmx-users] enery conserving problem in NVE simulations with SMW4-NPD polarizable force field

[Ding Yun]

Hello,

I'm trying to simulate liquid water (512 water molecules) with SMW4-NPD polarizable force field. The NVT simulation looks fine, but when I restart it with NVE runs, the total energy of the system keeps drifting down.

 The time step I'm using now is 0.5 fs and emtol=0.01 kJ/mol/nm. Gromacs is also compiled with double precision.  Does anyone have any suggestions for this kind of problem? Thanks a lot.

Regards,
Yun


My .mdp file:

; RUN CONTROL PARAMETERS
integrator               = md
tinit                    = 800
init_step                =0
dt                       = 0.0005 ; time step (ps)
nsteps                   = 400000  ; number of steps

; OUTPUT CONTROL OPTIONS
nstenergy                = 100
nstxout                  =100


; NEIGHBORSEARCHING PARAMETERS
nstlist                  = -1
ns_type                  = grid
pbc                      = xyz
rlist                    = 1.24

; OPTIONS FOR ELECTROSTATICS AND VDW
coulombtype              = PME-Switch
rcoulomb                 = 1.05
rcoulomb_switch          = 0.85
vdw-type                 = shift
rvdw                     = 1.05
ewald_rtol               =1e-4


; OPTIONS FOR BONDS
constraints              = h-bonds
; Type of constraint algorithm
constraint-algorithm     = Lincs


; Polarizable model parameters
emtol = 0.01
niter = 20

; Temperature coupling
tcoupl                   = no

; pressure coupling

pcoupl                = no

; GENERATE VELOCITIES FOR STARTUP RUN
gen_vel                  = no