Pressure decreasing after npt equilibration

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Hello
i have one issue
the density is of my system during npt is nearly 1000kg/m3 , but for md production in npt ensemble
it is showing less then 1000kg/m3
i will share my npt.mdp as well as md production. mdp


; VARIOUS PREPROCESSING OPTIONS
title = NPT simulation (constant number, pressure and temperature)
cpp = /usr/bin/cpp
define = -DPOSRES

; RUN CONTROL PARAMETERS
integrator = md
dt = 0.002
nsteps = 1000000

; OUTPUT CONTROL OPTIONS
nstxout = 2500
nstvout = 2500
nstfout = 0
nstlog = 2500
nstenergy = 2500
nstxtcout = 2500
xtc_precision = 1000
xtc-grps = System
energygrps = system

; NEIGHBORSEARCHING PARAMETERS
nstlist = 10
ns-type = Grid
pbc = xyz
rlist = 1.0

; OPTIONS FOR ELECTROSTATICS AND VDW
coulombtype = pme
pme_order = 4
fourierspacing = 0.16
rcoulomb = 1.0
vdw-type = cut-off
rvdw = 1.0
ewald_rtol = 0.00001

; Temperature coupling
Tcoupl = v-rescale
tc-grps = system
tau_t = 1.0
ref_t = 300

; Pressure coupling
Pcoupl = Berendsen
Pcoupltype = Isotropic
tau_p = 1.0
compressibility = 4.5e-5
ref_p = 1.0
DispCorr = EnerPres
refcoord_scaling = com

; GENERATE VELOCITIES FOR STARTUP RUN
gen_vel = no ; Assign velocities to particles by taking them randomly from a Maxwell distribution
gen_temp = 300 ; Temperature to generate corresponding Maxwell distribution
gen_seed = 135962 ; Seed for (semi) random number generation.

; OPTIONS FOR BONDS
constraints = all-bonds
constraint-algorithm = lincs
continuation = yes
shake-tol = 0.0001

; VARIOUS PREPROCESSING OPTIONS
title = Production Simulation
cpp = /usr/bin/cpp

; RUN CONTROL PARAMETERS
integrator = md
tinit = 0 ; Starting time
dt = 0.002 ; 2 femtosecond time step for integration
nsteps = 5000000 ; 10 ns

; OUTPUT CONTROL OPTIONS
nstxout = 100000 ; Writing full precision coordinates d
nstvout = 100000 ; Writing velocities d
nstfout = 0 ; Not writing forces
nstlog = 50000 ; Writing to the log file
nstenergy = 1000 ; Writing out energy information
nstxtcout = 1000 ; Writing coordinates
xtc_precision = 1000
xtc-grps = system
energygrps = system

; NEIGHBORSEARCHING PARAMETERS
nstlist = 10
ns-type = Grid
pbc = xyz
rlist = 1.0

; OPTIONS FOR ELECTROSTATICS AND VDW
coulombtype = pme
pme_order = 4
fourierspacing = 0.16
rcoulomb = 1.0
vdw-type = cut-off
rvdw = 1.0
ewald_rtol = 0.00001

; Temperature coupling
Tcoupl = v-rescale
tc-grps = system
tau_t = 1.0
ref_t = 300
; Pressure coupling
Pcoupl = Parrinello-Rahman
Pcoupltype = Isotropic
tau_p = 2.0
compressibility = 4.5e-5
ref_p = 1.0
DispCorr = EnerPres
refcoord_scaling = com
; GENERATE VELOCITIES FOR STARTUP RUN
gen_vel = no
gen_temp = 300
gen_seed = 314629

; OPTIONS FOR BONDS
constraints = all-bonds
constraint-algorithm = lincs
continuation = yes
shake-tol = 0.0001

; Input file
;
cpp = /usr/bin/cpp
define = -DFLEXIBLE
constraints = none
integrator = steep
nsteps = 10000
;
nstxout = 2500
nstvout = 2500
nstfout = 0
nstlog = 2500
nstenergy = 2500

; Energy minimizing stuff
;
emtol = 10
emstep = 0.01
nstcomm = 1
ns_type = grid
rlist = 1.0
rcoulomb = 1.0
rvdw = 1.0
Tcoupl = no
Pcoupl = no
gen_vel = no
pbc = xyz
please resolve the problem

the pressure in NVT is VERY sensitive to the precise volume. Thus, if you start an NVT simulation with the final structure of an equilibrated NPT run, you can easily end up with pressures far from the one used in the NPT simulation, 100 bar up or down is not uncommon. In most cases, if your pressure is off by a few tens of bars, you can ignore that. If you still want to make sure to get close to the desired pressure you can modify the box dimensions in the input structure file for the NVT to have exactly the average values from the NPT run, then do another short minimization+equilibration in NVT before starting production (this only works if the differences between the box dimensions of the final NPT structure and these averages are small (< 1 A), in this case you also want to make sure to use a structure that has no molecules broken across periodic boundaries), but i repeat, usually you do not need to bother….

Thanks for your reply
can you please check my mdp file and verify if any correction needed?
and please give the solution for the same.