[lammps-users] fix_deform & viscosity

Dear All,

I am trying to calculate the viscosity of one fluid with the fix_deform, particularly I want to observe a linear relationship between the applied shear rate and the shear stress. I am performing the simulations for specific density and temperature where i know from the literature the expected slope between shear stress and shear rate. I have performed several simulations with not any successful results.
I would really appreciate your advice.

My input file is the following (I am using the last update of lammps 1Nov)

2d NEMD simulation

units lj
atom_style atomic
dimension 2d

lattice sq 0.81
region box prism 0 100 0 20 -0.5 0.5 0 0 0
create_box 2 box
create_atoms 1 box
mass * 1.0

velocity all create 1.4 87287 loop geom

pair_style lj/cut 2.2
pair_coeff * * 1.0 1.0 1.0

neighbor 0.3 bin
neigh_modify delay 0 every 1

fix 1 all nvt/sllod 1.4 1.4 1
fix 2 all deform 1 xy erate 5e-3 remap v

timestep 0.001

compute 1 all stress/atom
compute 2 all sum 1

dump 1 all custom 500 dump.lammpstrj tag type x y z c_1[4]
#dump 2 all custom 500 x c_2[2]

thermo_style custom step atoms temp press pxy
#thermo_style custom step atoms temp press c_2[1] pxy c_2[4]

thermo 1000

run 30000

Is the simulation working? Are your viscosities reasonable?
Maybe you are in a regime where the viscosity is constant
instead of linearly changing? Send an emai to Pieter
in' t Veld (veld at verizon.net) or Matt Peterson (mkpeter at
sandia.gov). They do this kind of modeling with LAMMPS.