Hello,
I want to calculate the diffusion coefficient of azote in In0.1Ga0.9N . I used compute msd in lammps but but the curve is not linear and different with article. this my input file:units metal
dimension 3
boundary p p p
atom_style atomic
read_restart file.restart.100000000
#group delete id 7516
#delete_atoms group delete
#region delete block 0.0 57.1409188377 0.0 76.977424703 0.0 31.1035765747
#delete_atoms porosity delete 0.05 45348
group Ga type 2
group N type 1
group In type 3
#pair_style polymorphic
#pair_coeff * * InGaN_sw.poly N Ga In
#pair_style sw
#pair_coeff * * GaNAl.sw Ga N Al
pair_style sw
pair_coeff * * InGaN.sw N Ga In
neighbor 2.0 bin
neigh_modify delay 10 check yes
timestep 0.001
compute new all temp
#delete_atoms overlap 0.1 all all
#velocity all create 3100 12345 temp new
#fix F1 all box/relax iso 0 vmax 0.01 fixedpoint 0 0 0
fix 1 all npt temp 3100 3100 0.1 iso 0.0 0.0 1
compute mymsd N msd
thermo 100000
thermo_style custom step ke etotal temp vol lx ly lz c_mymsd[4]
#fix msdout N ave/time 100000 1 100000 c_mymsd[4] file msd1.out
#dump msdout all custom 100 msd.out c_mymsd[4]
dump MyDump all custom 10000000 dump.atoms id type x y z vx vy vz fx fy fz
dump position all custom 100000 dump.xyz id type x y z
#min_style cg
#minimize 1.0e-10 1.0e-10 5000 10000
restart 100000000 file.restart
run 10000000
#fix F1 all box/relax iso 0 vmax 0.01 fixedpoint 0 0 0
variable cohesive_energy equal pe/atoms
#variable a equal "lx/
#variable c equal "lz/
print “Calculated cohesive energy: ${cohesive_energy} eV/atom”
any suggestion!