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

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Sat, 24 Jun 2017 13:00:08 -0400

On Fri, Jun 23, 2017 at 11:07 PM, 高瞻 <sandy950111@...24...> wrote:
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:

​please try the latest patch (23 June 2017), which contains multiple bugfixes for tip4p pair styles that have accumulated since the version you are using and check if the issue persists. in case it does, please provide ​the data file, so the LAMMPS developers are check and try to reproduce what you are observing to be able to debug it.



# 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.

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Dr. Axel Kohlmeyer  akohlmey@...12...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.