# sample LAMMPS input script for viscosity of 2d LJ liquid
# Green-Kubo method via fix ave/correlate

# settings

variable	x equal 20
variable	y equal 20

variable	rho equal 0.6
variable        t equal 1.0
variable	rc equal 2.5

variable    p equal 400     # correlation length
variable    s equal 5       # sample interval
variable    d equal $p*$s   # dump interval 

# problem setup

units		lj
dimension	2
atom_style	atomic
neigh_modify	delay 0 every 1

lattice         sq2 ${rho}
region          simbox block 0 $x 0 $y -0.1 0.1
create_box      1 simbox
create_atoms    1 box

pair_style      lj/cut ${rc}
pair_coeff      * * 1 1

mass            * 1.0
velocity        all create $t 97287

# equilibration run

fix             1 all nve
fix	        2 all langevin $t $t 0.1 498094
fix	        3 all enforce2d

thermo          $d
run	        10000

velocity	all scale $t

unfix		2

# Green-Kubo viscosity calculation

reset_timestep  0

variable         pxy equal pxy

fix              SS all ave/correlate $s $p $d &
                 v_pxy type auto file profile.gk.2d ave running

variable         scale equal 1.0/$t*vol*$s*dt
variable         v11 equal trap(f_SS[3])*${scale}

thermo_style     custom step temp press pxy v_v11

run              500000

variable         eta equal v_v11
print            "running average viscosity: ${eta}"