Hi everyone,
I am trying to study the absorption of water with graphene using ReaxFF at 1200 K, but somehow I don’t see any interaction. I will put my code here to see what is wrong with my code. also, I have attached a jpg file regarding the initial visualization.
echo both
units real
atom_style full
dimension 3
boundary p p p
read_data graphene-water.data
pair_style reax/c NULL checkqeq yes
pair_coeff * * C-H-O.reax C H O
neighbor 2.0 bin #2 because the default parameter for skin is 2 in real units
neigh_modify every 1 delay 0 check yes
fix charge all qeq/reax 1 0.0 10.0 1e-6 reax/c
timestep 0.25
#---------------------ReaxFF Minimization---------------------------------
thermo 10
thermo_style custom step temp pe ke density press pxx pyy pzz lx ly lz
fix minconn all reax/c/bonds 100 emin_bonds.reaxc
minimize 1.0e-16 1.0e-6 40000 40000
min_style cg
unfix minconn
----------- Thermal Equilibrium----------
variable temp1 equal 1200.0
velocity all create ${temp1} 4921829
fix 1 all nvt temp 1200.0 1200.0 100.0 drag 0.2
#fix 1 all npt temp 700.0 700.0 100.0 iso 0.0 0.0 1000.0
fix 2 low_f setforce 0.0 0.0 0.0
fix 3 all qeq/reax 1 0.0 10.0 1.0e-6 reax/c
fix 5 all reax/c/bonds 1000 bonds.txt
compute 2 all temp
dump 1 all custom 1000 dumpsys.lammpstrj id type x y z
#dump 2 all cfg 10000 dump.minimization*.cfg mass type xs ys zs
#dump_modify 2 element C H O
thermo_style custom step pe etotal temp c_2
thermo 100
run 5000000
Any help will be appreciated.
Hi everyone,
I am trying to study the absorption of water with graphene using ReaxFF at 1200 K, but somehow I don't see any interaction. I will put my code here to see what is wrong with my code. also, I have attached a jpg file regarding the initial visualization.
i suspect a deeper, conceptual problem. two questions:
- why do you think there should be a significant interaction between
water and graphene at such a high temperature way above the boiling
point?
- which specific ReaxFF parameter set are you using? is this by any
chance the Chenoweth parameter set from 2008?
axel.
there is Zero interaction at 700 K and 1200 K,
yes this is the ReaxFF parameter from 2008 and there has been some papers published with this reaxff for 2300 K and there is significant interaction between them.
Do you think the problem is the reaxFF? I have tried it with different reaxFF and the same problem exist. Also, When I relax the structure the water molecules, aggloemerate.
Thanks for you help.
there is Zero interaction at 700 K and 1200 K,
that doesn't answer my question. why do you think there *should* be
adsorption at those temperatures?
yes this is the ReaxFF parameter from 2008 and there has been some papers published with this reaxff for 2300 K and there is significant interaction between them.
Do you think the problem is the reaxFF? I have tried it with different reaxFF and the same problem exist. Also, When I relax the structure the water molecules, aggloemerate.
the chenoweth parameter set is designed for combustion reactions,
which are - as you have noted - at much higher temperatures. that is
*very* different from what you say you want to be studying.
the way you have to pick a suitable ReaxFF parameter set, is that you
check out which system and conditions the parameter set was trained
for (there should be a publication describing the training process and
some reference results), and *not* be trying out different parameter
sets that happen to contain the elements of interest.
axel.
1200 K is high temperature and in that temperature there should be at least some reactions, and the possibility of a reaction is high at high temperatures, But rather in my simulation , no reaction happens and this is strange, I have tried the same simulation with the same reaxFF for oxygen and there is significant reaction with graphene. while this didnt happen for water.
Do you think that I should look for another ReaxFF ? and my inout code is fine?
Thanks for you help.
1200 K is high temperature and in that temperature there should be at least some reactions, and the possibility of a reaction is high at high temperatures, But rather in my simulation , no reaction happens and this is strange, I have tried the same simulation with the same reaxFF for oxygen and there is significant reaction with graphene. while this didnt happen for water.
that is the chemical behavior, that i would expect. (pure) oxygen is
*much* more reactive than water. you have to argue better. also, keep
in mind, that you are looking at very short time scales and length
scales. so even if thermodynamics would confirm, there should be
reactions, you also have to determine, whether they are not
kinetically very improbable to happen at the time and length scales,
you are looking at.
Do you think that I should look for another ReaxFF ? and my inout code is fine?
it is pointless to argue technical details before you have convincing
arguments, that the chemistry, thermodynamics and kinetics of the
compounds you are looking at, supports your claim.
axel.
There is this paper :# Hydrogen Bond Networks in Graphene Oxide Composite Paper: Structure and Mechanical Propertiesthat they have hydrated multilayer of graphene using the same ReaxFF at 1000 k
that is why I am concerned why I can’t reproduce their results.
that is *not* what this paper says. they have *assembled* graphene
oxide (GO) platelets (!) with multiple compositions into multi-layer
structures and *then* done MD simulations with those supercells.
there is *no* mentioning of plain graphene sheets and water, so you
are not even close to reproducing those simulations.
axel.
I have simplified my model and done the simulation. But the question still remains: why I should not get any interaction with the simple model I created?
Thanks for your suggestions.
I have simplified my model and done the simulation. But the question still remains: why I should not get any interaction with the simple model I created?
you are trying to compare apples with oranges and keep asking
questions that are not properly justified and thus make no sense to
me. i have no further comments.
axel.