strain effect on primary radiation damage

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1

Dear LAMMPS users
i want to see strain (uniaxial and hydrostatic) effect on primary radiation damage. i used fix deform command as follows:

Store final cell length for strain calculations

variable tmp equal “lz”

variable L0 equal ${tmp}

print “Initial Length, L0: ${L0}”

DEFORMATION

reset_timestep 0

fix relax all nvt temp 300 300 1

variable srate equal 1.0e10

variable srate1 equal “v_srate / 1.0e12”

fix 2 all deform 1 z erate ${srate1} units box remap x

variable strain equal “(lz - v_L0)/v_L0”

variable p1 equal “v_strain”

fix def1 all print 100 "timestep ${p1} " file Al_100.def1.txt screen no

dump strain all custom 100 dump.pos_strain.*.dat id type x y z vx vy vz

Display thermo

thermo 100
thermo_style custom step v_strain temp vol ke pe press

run 1000

#Starting PKA run

reset_timestep 0
unfix relax
unfix 2
unfix def1
undump strain

Make boundary atoms fixed

velocity boundary set 0.0 0.0 0.0

…
…
…
but in output i got that strain continuous to increase.
output looks as follows:

run 1000
Memory usage per processor = 121.087 Mbytes
Step v_strain Temp Volume KinEng PotEng Press
0 -2.3037689e-015 296.29855 1877733.1 4136.3178 -381917.8 320.92044
100 0.005 293.1684 1887121.8 4092.621 -381836.58 -3112.3114
200 0.01 291.87574 1896510.5 4074.5755 -381743.03 -6493.0218
300 0.015 288.95104 1905899.1 4033.7468 -381595.33 -9572.9171
400 0.02 287.88627 1915287.8 4018.8826 -381442.41 -12567.967
500 0.025 284.90018 1924676.5 3977.197 -381235.09 -15257.786
600 0.03 282.77329 1934065.1 3947.5056 -381014.32 -17819.607
700 0.035 282.10727 1943453.8 3938.208 -380790.67 -20348.147
800 0.04 280.77037 1952842.5 3919.5449 -380536.32 -22630.945
900 0.045 278.92129 1962231.1 3893.7319 -380255.03 -24719.269
1000 0.05 278.2035 1971619.8 3883.7115 -379971.37 -26736.306

but i want to apply for example 1% tensile strain and then equilibrate/ relax system at this strain. so your kind suggestion/solution how should i do this?

Thanx in advance
Kiakrn

2

you are applying a strain rate, not a constant strain. That is expected to have the strain in you system increased during a run. To my opinion, you have two solutions: 1 - apply the strain once, with the command change_box (do not forget to remap atoms coordinates), and then perform you dynamics. 2 - apply the strain with a strain rate, with the command fix deform followed by a dynamics (strain rate and dynamic duration should give you the desired strain). Then, after reaching the desired strain, perform a dynamics without the fix.