lammps-users Digest, Vol 75, Issue 64

I am going to apply tensile stress to diamond structure with temperature. More specifically i am going to do this process: 1-increasing temperature to 1000K, 2-realxation, 3-applying tensile stress, 4-relaxation.
I would like to know if “minimize command” can be used for these ralaxation?
I used “minimize” for zero temperature, but for the problem with temperature should I edit or add some other commands?

Steps 2 and 4 can be done via minimization. Step 3
can be done by using fix deform to change the box size.


Dear Steve,

thank you very much for your solution.
I did as you told me: first I start with a system with 1000K temperature (using fix nvt), then I used minimization to relax the system, after that for applying tensile stress i couldn’t use fix deform because i have static boundry condition, so i used “displace_atoms”. (my “in” file is attached here). could you please tell me I did correctly or not (specially the “run” after “displace_atom”?
And about the temperature : is this the right method or should I increase the temperature form zero to 1000K?

Best regards,

#Si geometry creation, relaxation and tensile stress

#set dimension and boundry condition
dimension 3
boundary s s s

#set units type,atom type and neigborhood
units metal
atom_style atomic
neigh_modify every 1

#create big box
lattice diamond 5.465
region big block -12 12 -12 12 -12 12
create_box 1 big

#create main atoms
lattice diamond 5.465
region main block -2 2 -2 2 -2 2
create_atoms 1 region main

#create sefr region
region sefrsefr block -2 -1.7 -2 2 -2 2
group sefr region sefrsefr

#create bist region
region bistbist block 1.7 2 -2 2 -2 2
group bist region bistbist

#set the mass of atoms
mass 1 28.0855

#set the velocity of atoms
velocity all create 1000.0 4928459 rot yes mom yes

#set the velocity of atoms of left and right to zero
velocity sefr set 0.0 0.0 0.0
velocity bist set 0.0 0.0 0.0

#set forces to sefr and bist
fix 144 sefr setforce 0.0 0.0 0.0
fix 155 bist setforce 0.0 0.0 0.0

#define the tersoff potential
pair_style tersoff
pair_coeff * * Si.tersoff Si

#set timestep
timestep 0.001

#compute stress per atom and potential per atom
compute stress all stress/atom pair
compute poten all pe/atom pair

#specify values to show in run
thermo 1000
thermo_style custom step temp pe ke etotal press

#specify the method of calculation
fix 10000 all nvt 1000.0 1000.0 0.001
run 100000

minimize 1.0e-12 1.0e-14 100000 100000

#strain load 1
displace_atoms bist move 0.191275 0 0 units box
run 100000

minimize 1.0e-12 1.0e-14 100000 100000

sorry, I don't debug other people's input scripts.
You need to answer these questions yourself by
visualizing the movement of the atoms and monitoring
thermo output, like the temperature.