[lammps-users] strain-stress


Hello ,lammps users and developers.
I want to simulate cu naowire elongation.My input file as follow:
#########Compute Cu nanowire stress##########
#define geometry
units metal
boundary p s s
atom_style atomic
lattice fcc 3.61
#define atom
region box block 0 30 0 3 0 3
create_box 1 box
create_atoms 1 box
mass 1 63.546
#define potentials
pair_style eam
pair_coeff * * Cu_u3.eam
neighbor 2.0 bin
neigh_modify delay 5
#define groups
region 1 block INF 1 INF INF INF INF
group left region 1
region 2 block 29 INF INF INF INF INF
group right region 2
group boundary union left right
group mobile subtract all left
#initial state relax
velocity left set 0.0 0.0 0.0
compute p all pressure thermo_temp
variable pressx equal c_p[1]
variable pressy equal c_p[2]
variable pressz equal c_p[3]
thermo_style custom step temp etotal press v_pressx v_pressy v_pressz vol
dump 1 all atom 1000 dump.tensile
minimize 1.0e-6 1.0e-6 1000 1000

fix 1 left setforce 0.0 NULL NULL
fix 2 all npt temp 1.0 1.0 1.0 x 0.0 0.0 10.0 drag 1.0
thermo 1000
timestep 0.002
run 60000
#stress
unfix 2
fix 3 all nve
fix 4 all temp/rescale 100 1.0 1.0 5 1.0
fix 5 all deform 1000 x erate 0.002 units box
compute s all stress/atom
compute strea all reduce sum c_s[1]
variable stressa equal c_strea/vol
compute streb all reduce sum c_s[2]
variable stressb equal c_streb/vol
compute strec all reduce sum c_s[3]
variable stressc equal c_strec/vol
thermo_style custom step temp press v_stressa v_stressb v_stressc vol
thermo_modify lost ignore
run 300000

my log file as follow;
Step Temp TotEng Press pressx pressy pressz Volume
10 0 -4766.7741 -9467.401 -28805.101 201.44924 201.44924 12656.176
1000 5.8577493 -4813.7388 -9783.3679 675.80509 -15012.954 -15012.954 12580.482
2000 7.9550326 -4815.9905 -1068.657 82.956196 -1642.0382 -1646.8889 13475.069
3000 21.107294 -4840.1038 -9.3748328 -146.47693 3461.2616 -3342.9091 14840.202
4000 8.7574278 -4850.6306 -499.80941 -301.50878 -370.47586 -827.44361 14074.184
5000 3.636028 -4852.338 337.20922 54.720254 1188.7142 -231.80678 14079.159
6000 2.4843546 -4852.8725 136.37384 149.85908 252.49079 6.771638 14073.178
7000 1.6864251 -4853.1131 15.662507 72.548409 -65.169166 39.608279 14074.059
8000 1.5206638 -4853.2419 107.93858 16.524965 66.713626 240.57716 14075.637
9000 1.3079775 -4853.3171 -178.71515 -122.77549 -595.89009 182.52015 14073.878
10000 1.1551918 -4853.3632 -184.78916 -91.380914 -248.05545 -214.9311 14075.901
11000 1.0607825 -4853.3912 -89.872927 -129.6888 -257.3616 117.43162 14076.737
12000 1.0325261 -4853.4077 -49.110891 -10.659037 -164.51197 27.838333 14075.808
13000 1.0092817 -4853.4168 -167.14715 16.857193 -22.676863 -495.62178 14075.765
14000 0.97762614 -4853.42 -145.84234 -37.452718 -378.73731 -21.336994 14074.407
15000 0.98629519 -4853.4201 73.832016 -82.751934 144.28006 159.96792 14075.828
16000 0.99426418 -4853.4201 -32.400337 -76.786215 -55.490885 35.076088 14074.626
17000 1.0168626 -4853.4203 13.622314 14.259124 -182.23369 208.84151 14073.54
18000 1.0136947 -4853.4204 192.82091 77.457135 469.81272 31.19286 14075.298
19000 1.0044853 -4853.4202 -69.219932 53.008899 -38.944557 -221.72414 14073.084
20000 0.99374787 -4853.4202 -41.213038 13.937728 95.311986 -232.88883 14075.075
21000 0.99091944 -4853.4203 113.86738 -4.5213623 218.86814 127.25535 14076.776
22000 1.0232208 -4853.4201 -158.07804 -9.1490105 -389.03808 -76.04704 14073.496
23000 0.9849583 -4853.4198 -118.4683 120.71077 -120.80578 -355.3099 14074.092
24000 1.0335818 -4853.4198 -32.974225 24.92525 -307.70436 183.85643 14074.967
25000 0.98957023 -4853.42 -27.467711 32.649555 -218.40353 103.35084 14074.825
26000 1.0784292 -4853.42 -67.161189 -6.4060894 63.001164 -258.07864 14075.321
27000 1.0522253 -4853.42 53.292941 163.25896 -62.495159 59.115024 14073.006
28000 1.0226748 -4853.4204 127.85812 98.506569 404.00695 -118.93917 14074.733
29000 1.0233257 -4853.4204 32.504367 74.964307 130.98531 -108.43652 14074.256
30000 0.9944461 -4853.4205 196.95316 60.71902 136.77011 393.37034 14074.711
31000 1.008883 -4853.4202 192.8468 26.977387 417.97315 133.58987 14075.599
32000 0.97439472 -4853.4202 -178.01944 -36.979125 -383.85248 -113.22673 14073.353
33000 1.0001296 -4853.4201 -97.362245 -192.90233 -156.91394 57.72953 14076.926
34000 1.0348805 -4853.4199 110.7748 -30.887517 118.3641 244.84782 14076.868
35000 1.0573359 -4853.4197 -48.950402 -71.543514 -152.54397 77.236283 14074.876
36000 1.049009 -4853.4198 20.384265 -43.401839 257.77032 -153.21569 14076.83
37000 1.0363447 -4853.4201 -3.3339125 -54.000178 -46.40198 90.40042 14075.63
38000 1.0192182 -4853.4201 68.644699 66.633759 212.08251 -72.782174 14073.993
39000 1.0031841 -4853.4202 156.08489 45.055115 435.93823 -12.738657 14074.904
40000 1.0162736 -4853.4204 79.565537 -132.0996 -21.487111 392.28332 14074.8
41000 1.0023149 -4853.4206 35.72229 -17.765844 260.14211 -135.20939 14074.731
42000 1.0226967 -4853.4203 26.279595 148.33517 40.4297 -109.92608 14073.004
43000 0.97332487 -4853.4201 69.303772 -100.98674 50.371087 258.52697 14076.151
44000 0.99904273 -4853.4199 9.132157 -176.45555 268.55427 -64.702247 14078.074
45000 0.99277676 -4853.42 -122.56189 83.923411 -317.75339 -133.85567 14074.297
46000 1.028274 -4853.4199 82.175108 198.31878 30.646469 17.560072 14075.143
47000 0.99873802 -4853.4197 11.682738 131.56852 -102.58042 6.0601213 14074.392
48000 1.0056234 -4853.42 -116.18853 23.046548 -482.14307 110.53094 14073.451
49000 1.0195711 -4853.4202 186.43575 196.81176 190.14245 172.35303 14075.019
50000 0.99899038 -4853.4203 63.498175 106.75933 -26.598832 110.33403 14073.559
51000 1.0023758 -4853.4202 -92.953838 4.0156007 76.168153 -359.04527 14073.878
52000 0.99055311 -4853.4203 51.134329 16.117817 303.05102 -165.76585 14076.069
53000 1.0304976 -4853.4203 116.98557 54.259969 -23.846222 320.54296 14074.865
54000 1.0006526 -4853.4202 -14.898359 27.017106 88.626935 -160.33912 14074.928
55000 1.0119442 -4853.42 -178.16771 -88.825336 -399.71291 -45.964894 14074.029
56000 0.99722267 -4853.4199 -67.894494 -3.296107 -418.97688 218.58951 14074.289
57000 1.0080066 -4853.42 -24.676099 12.260302 -9.8617161 -76.426882 14075.612
58000 0.99701359 -4853.42 -178.94893 -113.2989 -374.9793 -48.568575 14075.1
59000 0.98600839 -4853.4199 -37.115121 -85.630288 86.435583 -112.15066 14077.294
60000 0.98786471 -4853.4202 -112.77874 -35.505223 44.284938 -347.11593 14075.502
60010 0.97579653 -4853.4202 -75.096918 43.976049 83.154032 -352.42083 14074.687

Though run such a long time the press vibrate heavily and can’t go to zero .
I want to know how can I let the press not vibrate and get fixed.


Thanks
Best regards





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If you pull on a system, the pressure will never
be exactly 0.0. You’re perturbing the system
very fast, very hard (in real time units) and pressures
fluctuate.

Steve