NEMD simulations in nanofluids

Dear Sir,
I am applying the NEMD simulations for the calculating the thermal conductivity of nanofluids(Argon fluid with Copper Nanoparticle). The following is my input file(5% loading), but the result doesn’t show the increasement with the nanoparticle’s loading. Is there anything wrong with my input file?
Thanks a lot.

Jie Liu

MD simulation of Ar-5%Cu thermal conductivity, steps–Initialization, NEMD, Statistic


units lj
newton on
boundary p p p
atom_style full
neighbor 0.3 bin
neigh_modify check yes

lattice fcc 0.844
region box block -4 4 -4 4 -4 4 units lattice
create_box 2 box
create_atoms 1 box
region sphere sphere 0.0 0.0 0.0 1.8283126 units lattice
delete_atoms region sphere
lattice fcc 3.35214
create_atoms 2 region sphere

replicate 1 1 32

group ar type 1
group cu type 2

lattice fcc 0.844

mass 1 1.0
mass 2 1.590639

pair_style lj/cut 2.6
pair_modify mix arithmetic
pair_coeff 1 1 1.0 1.0 # LJ parameters for Ar-Ar
pair_coeff 2 2 39.2964071856 0.686549 # LJ parameters for Cu-Cu

minimize 0.0 0.0 100000 100000 #@@@@@@@@@@@@@@

variable boltz0 equal 1.3806504e-23
variable sigma0 equal 3.405e-10
variable episilon0 equal 1.67e-21
variable mass0 equal 6.63385e-26
variable dt equal 0.002

NEMD Displacement

region up block -4 4 -4 4 124 128 units lattice
region down block -4 4 -4 4 -4 0 units lattice


fix nvt all nvt temp 0.71 0.71 0.2

compute ke all ke/atom
variable temp atom c_ke/1.5
fix temp_profile all ave/spatial 1 900000 900000 z lower 4 v_temp file temp_profile.dat units lattice

compute up_temp all temp/region up
compute down_temp all temp/region down
variable delta_temp equal c_up_temp-c_down_temp
fix delta_out all ave/time 1 900000 900000 v_delta_temp file delta_temp.dat

variable ke equal ke
variable pe equal pe
variable etotal equal etotal
variable lx equal lx
variable ly equal ly
variable lz equal lz
variable step equal step
thermo_style custom step temp ke pe etotal lx
thermo 100000

timestep ${dt}
run 999999


variable swap equal 4500
fix heat_swap ar thermal/conductivity ${swap} z 64
fix e_exchange ar ave/time 900000 1 900000 f_heat_swap file e_exchange.dat

variable tc equal f_e_exchange/(4.0*{dt}*(step-999999)*{lx}{ly}*f_delta_out/{lz})sqrt({episilon0}/{mass0}){boltz0}/({sigma0}${sigma0})
fix tc_out all ave/time 900000 1 900000 v_tc file tc.dat

run 18000000

It's impossible for anyone to stare at a complex input script
and magically determine why it is giving a result slightly
different than you expect. You have to treat it like
a debugging problem. Start with a simple problem, add
options one at a time, verify that the option is doing what
you expect, verify that the answer is correct, etc.

There is no one better to do that than you.