Hi, Steve:
I set up a simple orthogonal box whose three parameters are 1.81nm*1.81nm*5.05nm, the atoms are all Cu. I want to use the "displace_box" to give the box an initial strain in z direction. My in.* file is as below:
# 3d Cu100
#Initialization
units metal
atom_style full
#Atom definition
read_data data.Cu100
#Force-field
pair_style eam
pair_coeff * * cuu3.eam
#Settings
group 1 id <= 100
group 2 id >= 1301
group 3 union 1 2
group 4 subtract all 3
variable l_z equal lz
variable lz0 equal \{l\_z\}
variable lz3 equal v\_lz0/100
minimize 0 0 100000 100000
reset\_timestep 0
fix 1 all npt 0\.001 0\.001 100 aniso 0 0 0 0 NULL NULL 1000 drag 1
run 5000
reset\_timestep 0
compute 1 all stress/atom
compute 2 all reduce sum c\_1\[3\]
variable stress equal c\_2/\(vol\*10^4\)
variable strain equal \(lz\-v\_lz0\)/v\_lz0
variable ratio equal lx/v\_lx0
fix 5 3 setforce 0 0 0
displace\_box all z delta 0 {lz3} units box
fix 3 all ave/time 1 200 1000 v_stress
thermo_style custom step v_strain f_3
thermo_modify flush yes
thermo 1000
run 71000
I am sure that the data.Cu100 and cuu3.eam are all OK, Because I have tried to change "displace_box" with "fix deform" command, and the data the programme gives accords with the experiment well. But what make me confused is that if I used the "displace_box" command, the mean stress of all the atoms in z direction is unstable, no matter how many times I run after the initial strain. Here is some part of my log file.
Step strain 3
0 0.01 0
1000 0.01 0.53821053
2000 0.01 0.83189227
3000 0.01 0.35370564
4000 0.01 1.0049092
5000 0.01 0.19629893
6000 0.01 1.1434605
7000 0.01 0.079951733
8000 0.01 1.2353194
9000 0.01 0.0148101
10000 0.01 1.2725684
11000 0.01 0.0063304946
12000 0.01 1.2522789
13000 0.01 0.054829905
14000 0.01 1.1767381
15000 0.01 0.15549704
16000 0.01 1.0532004
17000 0.01 0.29886284
18000 0.01 0.89319448
19000 0.01 0.47168094
20000 0.01 0.71145001
21000 0.01 0.65814357
22000 0.01 0.52454075
23000 0.01 0.84132553
24000 0.01 0.34936956
25000 0.01 1.004723
26000 0.01 0.2016375
27000 0.01 1.1337449
28000 0.01 0.094437803
29000 0.01 1.2170181
30000 0.01 0.037102365
31000 0.01 1.2473888
32000 0.01 0.034398824
33000 0.01 1.2225344
34000 0.01 0.086140292
35000 0.01 1.1451371
36000 0.01 0.18724051
37000 0.01 1.0226009
38000 0.01 0.32820742
39000 0.01 0.86634678
40000 0.01 0.49602504
41000 0.01 0.6907501
42000 0.01 0.67534836
43000 0.01 0.51181711
44000 0.01 0.849905
45000 0.01 0.34572268
46000 0.01 1.0039743
47000 0.01 0.20734638
48000 0.01 1.1238069
49000 0.01 0.10894142
50000 0.01 1.1988536
51000 0.01 0.059056433
52000 0.01 1.2226925
53000 0.01 0.061801298
54000 0.01 1.1935768
55000 0.01 0.116514
56000 0.01 1.1145565
57000 0.01 0.21785723
58000 0.01 0.99316456
59000 0.01 0.35633292
60000 0.01 0.84070142
61000 0.01 0.51916396
62000 0.01 0.67118453
63000 0.01 0.69146726
64000 0.01 0.50005855
65000 0.01 0.85761293
66000 0.01 0.34278533
67000 0.01 1.0026446
68000 0.01 0.21344566
69000 0.01 1.113629
70000 0.01 0.12348099
71000 0.01 1.1808106
What is the difference between "displace_box" and "fix deform" on change the shape of the box, except that the later is used for dynamics run?
Thank you~
Regards
Xu