[lammps-users] Water gold hybrid simulation

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1

Hi all,

I am still having trouble getting this simulation to run. I am getting
an error that my pair coefficient arguments are invalid. I have
specified the cutoff and made sure it is the same.

Can anyone see anything wrong with my input script??? Thanks...This is
shown below:

# Nanofluid simulation input script

dimension 3
units metal
boundary p p p

neighbor 0.3 bin
neigh_modify delay 5

atom_style full
kspace_style pppm/tip4p 1.0e-4

read_data dataNULLcharge.nanofluid

#Pair_style hybrid definition

pair_style hybrid lj/cut/coul/long/tip4p 2 1 1 1 0.1250 2.5 eam lj/cut 2.5

#Definition of pair coefficients

#Water

pair_coeff 1*2 1*2 lj/cut/coul/long/tip4p 0.0 0.0 2.5 #pair
coefficients for tip4p between OH (LJ parameters set to zero)
pair_coeff 1 1 lj/cut/coul/long/tip4p 0.0 0.0 2.5 #pair
coefficients for tip4p between HH (LJ parameters set to zero)
pair_coeff 2 2 lj/cut/coul/long/tip4p 0.16275 3.16435 2.5 #pair
coefficients for tip4p between OO

bond_style harmonic
bond_coeff 1 450.000000 1.000000 #still not sure about these. How
did you work out that K is 450.000000!

angle_style harmonic
angle_coeff 1 55.000000 104.52 #still not sure about these. How did
you work out that K is 55.000000!

#Gold

pair_coeff 3 3 eam Au_u3.eam #pair coefficients for gold - where did
this come from???

#Water and gold together

pair_coeff 1*2 3 lj/cut 2.5 #pair coefficients for interaction
between water and gold is this correctly defined???

group hydrogen type 1
group oxygen type 2
group gold type 3

group all union hydrogen oxygen gold

fix 1 all nve
fix 2 all temp/rescale 100 0.45 0.45 0.02 1.0
fix 3 all enforce2d

thermo 50
run 1000

Kind regards,

Folayo Osekita
MEng Student, Queen Mary, University of London

2

I suggest you (and everyone who posts questions where they
can't figure out what is wrong with their input script)
run your script with -echo screen as a command-line switch.
Then you will see this is the offending line:

pair_coeff 1*2 3 lj/cut 2.5

If you look at the doc page for lj/cut it says you need a epsilon and sigma
and an (optional) cutoff.

Steve

3

2009/1/28 Folayo Osekita <folayoosekita@…444…>

bond_style harmonic
bond_coeff 1 450.000000 1.000000 #still not sure about these. How
did you work out that K is 450.000000!

angle_style harmonic
angle_coeff 1 55.000000 104.52 #still not sure about these. How did
you work out that K is 55.000000!

It should also be pointed out that when working with SPC/E, TIP3P, and TIP4P water, unless it is meant to include a flexible potential, one should have a “fix shake” to constrain the bonds and angles in the water molecules. The original implementations of these molecules did not include bond and angle potentials, so any values reported for those quantities are either the result of someone’s reparameterization to include them, or are simply dummy values (placeholders needed to satisfy LAMMPS specification requirements, but ignored because of the use of “fix shake”).

–AEI