[lammps-users] graphene simulation

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1

Dear Sandia,

I am currently trying to calculate the thermal conductivity of different layers of graphene. I created multiple layer by using replicate command. However, when I perform two layers with nvt command at room temperature about 2 million timesteps, the two sheets from initially seperated far away come close together at equilibrate position. When I perform more layer graphene sheets, the graphene alone z-axis lost it's symmetry and at the beginning of z-axis the sheet seems are very close to each other while at the end of z-axis the seperation of the graphene via replicate is remained.

Can anyone point out there is any error of my simulation?

Here is the input script and image I attached:

dimension 3
boundary p p p
units metal

atom_style charge
read_data data.charge

region up block -9.838 -7.8704 INF INF INF INF units box
region down block 0 1.9676 INF INF INF INF units box

pair_style airebo 3.0 1 1
pair_coeff * * CH.airebo C

replicate 1 1 5

neighbor 4.0 bin
neigh_modify delay 0 every 1 check yes

timestep 0.00005

velocity all create 300 1234567 mom yes rot yes dist gaussian units box

fix thermostat all nvt temp 300.0 300.0 0.1

compute alltemp all temp
thermo_style custom step atoms temp press pe ke etotal xlo xhi ylo yhi zlo zhi vol enthalpy
thermo_modify temp alltemp lost warn

compute ke all ke/atom
variable temp atom c_ke/(1.5*1.0)/8.617343*100000.0
fix temp_profile all ave/spatial 1 100000 100000 x -9.838 1.9676 v_temp file temp6.profile units box
fix temp_atom all ave/atom 1 100000 100000 v_temp
compute up_temp all temp/region up
compute down_temp all temp/region down
variable delta_t equal c_down_temp-c_up_temp
fix delta_t all ave/time 1 100000 100000 v_delta_t file delta_t6.dat

dump 1 all xyz 100000 dump6.coord.*
dump 2 all custom 100000 dump6.vel.* id type mass vx vy vz fx fy fz f_temp_atom
restart 400000 restart6.mwnt.*
thermo 1000
run 400000

unfix thermostat
fix ensemble all nve
fix heat_swap all thermal/conductivity 40 x 10
fix e_exchange all ave/time 40 2500 100000 f_heat_swap file e_exchange6.dat

run 2000000

1-layer.png

2-layer_final.png

2-layer_initial.png

3-layer_final.png

3-layer_initial.png

5-layer_final.png

5-layer_initial.png

7-layer_final.png

7-layer_initial.png

2

Dear Sandia,

I am currently trying to calculate the thermal conductivity of different layers of graphene. I created multiple layer by using replicate command. However, when I perform two layers with nvt command at room temperature about 2 million timesteps, the two sheets from initially seperated far away come close together at equilibrate position. When I perform more layer graphene sheets, the graphene alone z-axis lost it's symmetry and at the beginning of z-axis the sheet seems are very close to each other while at the end of z-axis the seperation of the graphene via replicate is remained.

Can anyone point out there is any error of my simulation?

you description prompts to give you more questions rather than answers.

so what is the distance between the layers? and what is it supposed to be?

in which direction to you want to compute the thermal conductivity?

along the sheet or between the sheets?

axel.