Dear LAMMPS users
Recently I simulated an statistic water droplet with 6000 water molecule which located on graphene surface. I expected that the spherical shape of droplet ends up as hemispherical droplet and stays constant(without movement) after 1.5 nano seconds. However, the droplet moves place to place on the graphene sheet. I don’t know exactly it is related to fluid- structure interaction or there is a problem in my simulation. I will appreciate if someone could help me.
my input script:
units real
atom_style full
boundary p p f
special_bonds lj/coul 0.0 0.0 0.0
pair_style lj/cut/coul/long 10 9
bond_style harmonic
angle_style harmonic
kspace_style pppm 0.0001
kspace_modify slab 3.0
neighbor 2.0 bin
neigh_modify every 1 delay 0 check yes
fix sheet Cgraphene setforce 0.0 0.0 0.0
fix top CgrapheneUp wall/reflect zlo 158
fix fixnvtf fluidbox nvt temp 298.13 298.13 100.0
minimize 1.0e-4 1.0e-6 1000 1000
fix fixshake fluidbox shake 0.0001 20 10 b 1 2 3 a 1 2
run 1500000
regards
mehrab
Dear LAMMPS users
Recently I simulated an statistic water droplet with 6000 water molecule
which located on graphene surface. I expected that the spherical shape of
droplet ends up as hemispherical droplet and stays constant(without
movement) after 1.5 nano seconds. However, the droplet moves place to place
on the graphene sheet. I don't know exactly it is related to fluid-
structure interaction or there is a problem in my simulation. I will
appreciate if someone could help me.
i see no obvious mistakes in your input outside of using rather sloppy
convergence criteria for both kspace and shake.
these are barely acceptable for homogeneous bulk systems, where a lot
of error cancellation can happen, but for an inhomogeneous system like
yours, you probably want to make more conservative choices (e.g.
tighten to 1.0e-6). also, please explain, what is the benefit of
having the coulomb realspace cutoff shorter than the lennard-jones
cutoff?
other than that, please explain, what is your reasoning why should the
water droplet stay in place. you also fail to describe whether the
droplet does a "random walk" like motion or moves linearly.
have you discussed this with your adviser/supervisor?
axel.
Dear Axel
Thank you so much for your response.
i see no obvious mistakes in your input outside of using rather sloppy
convergence criteria for both kspace and shake.
these are barely acceptable for homogeneous bulk systems, where a lot
of error cancellation can happen, but for an inhomogeneous system like
yours, you probably want to make more conservative choices (e.g.
tighten to 1.0e-6). also, please explain, what is the benefit of
having the coulomb realspace cutoff shorter than the lennard-jones
cutoff?
I am trying to regenerate an article which this value was assigned there.
other than that, please explain, what is your reasoning why should the
water droplet stay in place. you also fail to describe whether the
droplet does a “random walk” like motion or moves linearly.
These movements are randomly.
have you discussed this with your adviser/supervisor?
Yes I did. He said " you might make a mistake in your simulation"
Dear Axel
Thank you so much for your response.
i see no obvious mistakes in your input outside of using rather sloppy
convergence criteria for both kspace and shake.
these are barely acceptable for homogeneous bulk systems, where a lot
of error cancellation can happen, but for an inhomogeneous system like
yours, you probably want to make more conservative choices (e.g.
tighten to 1.0e-6). also, please explain, what is the benefit of
having the coulomb realspace cutoff shorter than the lennard-jones
cutoff?
I am trying to regenerate an article which this value was assigned there.
other than that, please explain, what is your reasoning why should the
water droplet stay in place. you also fail to describe whether the
droplet does a "random walk" like motion or moves linearly.
These movements are randomly.
have you discussed this with your adviser/supervisor?
Yes I did. He said " you might make a mistake in your simulation"
ask him, if he has ever heard the term "brownian motion"?
axel.
Thank you so much Axel
I asked my advisor about that.
But Is there any way to omit this random movements? I mean is it possible to simulate regardless of Brownian motion?
Is it logical to use “fix momentum” command?