[lammps-users] lammps and electro-osmotic flow NEMD


I want to know whether I can do NEMD simulation about electro-osmotic flow with LAMMPS. In manual it olny say something about fluid’s rheological properties.
Thanks in advance.



Yes. NEMD simulation of EOF is possible with LAMMPS.

Here's an example input script:

units real
neigh_modify delay 5 every 1
boundary p p f
processors 4 4 3
atom_style full
bond_style harmonic
angle_style harmonic
pair_style lj/cut/coul/long 10
kspace_style pppm 1e-4
kspace_modify slab 3.0
read_restart restarts/xcacl2_silica_nanochannel.1000
pair_modify mix arithmetic
special_bonds 0.0 0.0 1.0 0.0 0.0 0.5
group water type 7 8
group calcium type 9
group chlorine type 10
group frozen molecule 2 10467
group flexible molecule 1 10466
group system union flexible water calcium chlorine
fix 1 system nvt 300.0 300.0 100.0
fix 2 system efield 0.001 0.0 0.0
fix 3 system wall/reflect zlo zhi
fix 4 frozen setforce 0.0 0.0 0.0
fix 5 all shake 1e-6 20 0 b 3 5 a 6
timestep 1.0
thermo 10000
thermo_style multi
thermo_modify flush yes
restart 50000 restarts/xcacl2_silica_nanochannel
dump 1 all atom 10000 dumps/atoms_cacl2_silica_nanochannel_*
dump_modify 1 image yes scale yes
dump 2 all custom 10000
dumps/velocity_cacl2_silica_nanochannel_* tag type vx vy vz
run 10000

Note the efield fix that imposes the electrostatic field. You'll need
to build your own system and data file, but can use a LAMMPS input
script similar to the one above.


Note that Paul's script uses PPPM. If you want to shear
the box as in other NEMD models, you can't use PPPM. The
only mixture of shearing and long-range Coulombics LAMMPS currently
allows is ewald/n.

You might also be able to use the fix viscosity command (in a non-sheared
box) to establish the gradient you want, or some variant on it.