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[lammps-users] Different outcomes with same *.data & *.in while changing the parallel core numbers
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[lammps-users] Different outcomes with same *.data & *.in while changing the parallel core numbers

From: 高瞻 <sandy950111@...24...>
Date: Sat, 24 Jun 2017 11:07:11 +0800

Hello everyone,

I use the TIP4P-2005 water model to simulate the two-phase process of water, but when I change the parallel core number from 100 to 20, the outcome of the simulation changes a lot. My LAMMPS version is lammps-17Nov16, and my input file is as follows:

# variables input

variable         DT equal 2.0              
variable         A equal 220               
variable         r equal 10                
variable         L equal 75                
variable         THERMO equal 5000              
variable         Pstart equal -0.5*10*$A
variable         Pstop equal -0.5*10*$A

# init

units            real
dimension        3
boundary         p p p
atom_style       full
timestep         ${DT}
neighbor         2.0 bin
neigh_modify     delay 0 every 1 check yes

# create geometry

pair_style       lj/long/tip4p/long long long 2 1 1 1 0.1546 9 8.5
kspace_style     pppm/disp/tip4p 1e-5
kspace_modify    force/disp/real 0.0001 force/disp/kspace 0.002 mix/disp geom 
bond_style       harmonic
angle_style      harmonic
read_data        data.droplet_npt

# variables output

variable         PRESS equal press
variable         VOL equal vol

# fixes 

fix              0 all indent 10.0 sphere $L $L $L $r units box
fix              1 all shake 0.0001 100 0 b 1 a 1
fix              barostat all npt temp 298.0 298.0 $(100.0*dt) iso ${Pstart} ${Pstop} $(1000.0*dt) drag 1.0
fix              print_press all print 1 "${PRESS}" file press.dat  screen no title ""
fix              print_vol all print 1 "${VOL}" file vol.dat screen no title ""

# run 

thermo_style     custom step temp press vol
thermo           ${THERMO}     
run              250000

The simulation is designed to mimic the cavitation in water at a low pressure, and the "outcome changes a lot" means the vol-time curves in the simulations are different. The vol variable in the 100 core simulation is increasing much quicker than in the 20 core simulation, which makes me confused.
What I want to ask for advice is that is there any other factors except the "floating point error" that cause this situation? Because I think the the "outcome change" in the two simulation is really beyond my expectation.