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[lammps-users] Request to add question to the forum (can not get high enough sp3 atoms while preparing amorphous carbon)
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[lammps-users] Request to add question to the forum (can not get high enough sp3 atoms while preparing amorphous carbon)


From: Shahriar Mufid <shahriar238@...24...>
Date: Thu, 14 Sep 2017 17:34:03 -0500

Hello,

My research is related to the molecular dynamics simulation of amorphous carbon (a-C). Recently I had to prepare amorphous carbon containing different amount of sp2/sp3 atoms. So I tried the method described in this paper (http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7738454) where they followed the method of preparing a-C from their previous paper published in 2013 (https://doi.org/10.1016/j.apsusc.2013.09.073). I followed the same procedure using airebo potential, but unfortunately I could not get such high percentage of sp3 atoms in the prepared a-C. For instance, when I used density of 2.8g/cc (20A*20A*20A box, 1122 atoms), I got less than 20% sp3 atoms while the paper reported 64.58% sp3. 

I have included my input file below. Would you kindly have a look and let me know what I did wrong?

Your help is highly appreciated. Thank you very much for your consideration.



My input file:


# Lammps version: LAMMPS (9 Dec 2014)
# ----------------------------
units metal
dimension 3
boundary p p p
atom_style charge
# --------------------------------------
region box block 0 20 0 20 0 20 units box
create_box 1 box
create_atoms 1 random 1122 964723 box
mass 1 12.0107
group all region box
set type 1 charge 0
# -----------------------------------
pair_style airebo 3 1 1 
pair_coeff * * CH.airebo C
# -----------------------------------
minimize 1.0e-8 1.0e-8 1000000 1000000
reset_timestep 0
timestep 0.00025

fix 1 all langevin 300 300 0.025 9536418
fix 2 all nve

thermo_style custom step temp press vol enthalpy ke pe etotal lx ly lz density atoms
thermo_modify lost warn
thermo 1000
run 20000

unfix 1
fix 1 all langevin 300 8000 0.025 7268134
run 40000

unfix 1
fix 1 all langevin 8000 8000 0.025 541397
run 8000

unfix 1
fix 1 all langevin 8000 300 0.025 9536418
run 8000

unfix 1
fix 1 all langevin 300 300 0.025 9536418
dump 2 all custom 10000 dlc_final.dump id type q x y z vx vy vz
compute 1 all coord/atom 1.75
dump 4 all custom 10000 coordination.dump c_1
run 20000

Best regards,
Shahriar Mufid Rahman,,
Texas Tech University,
Lubbock, TX, 79415.



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