[lammps-users] How to relax the wurtzite structure

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1

Hello,
I want to relax the wurtzite structure by SW polymorphic potentiel.
how can we relax this structure?
when I try to do simulation withlammps, I don’t get the same energy found in the article , so I can’t find the solution.
Any help?

#atom_modify

P2 setup box and create atoms and groupen atoms

read struct.data

read_data perfect.dat

replicate 3 3 3

neighbor 2.0 bin
neigh_modify delay 0 every 1 check yes

P3 Potential config: Pair style for atomic interactions

pair_style polymorphic
pair_coeff * * GaN_sw.poly N Ga
#pair_style sw
#pair_coeff * * GaN.sw N Ga

timestep 0.001

P4 Define and initialize atomic configuration

#fix F1 all box/relax aniso 0 vmax 0.01 fixedpoint 0 0 0

#velocity all create 0.0 761341
#run 1000

#velocity all create 300.0 761341

P4 Fixes for time integration and constraints

thermo 100
thermo_style custom step temp press etotal vol lx ly lz

variable cohesive_energy equal pe/atoms

run 0

print “Calculated cohesive energy: ${cohesive_energy} eV/atom”

compute atmE all pe/atom
dump D1 all custom 1000 rlx_struct.dump.* id type x y z fx fy fz c_atmE

run 0

P5 Run or minimize

#min_style cg
minimize 1.0e-15 1.0e-15 1000 10000

write_dump all custom sorted_rlx_struct.lammps id type x y z c_atmE modify sort id

write_data rlx_struct.*.lammps
write_data rlx_struct.lammps

2

are you sure you have the correct geometry? and the correct units?

3

Yes, they are correct.

4

If you have the exact same geometry and the same potential file and the same units then you should get the same energies.
It is impossible to tell from remote what is the exact reason for any differences.
Please note that you posted a significantly incorrect geometry in a previous post, so the chances are that there is still a mistake.

5

this is the input file

perfect.dat (790 Bytes)

in.LattCont (1.64 KB)

6

ok. that looks reasonable and running the minimization will only result in minor changes.
So how is the energy of this system then different from the result that you are comparing to? Did they report the global energy for a given number of unit cells or an energy per GaN unit?
did the original authors also use LAMMPS, and if yes, which version?

7

The target value is -4,401 ev/atom and the value obtained -4.34 ev/atom.

8

at this point there is nothing much that can be done from remote.
either there is a difference in a detail that can only be found out from studying the paper carefully (again) or there is something that can only be answered by the authors of the paper.