there is no force when i used the hybrid pair_style

because when i use a cutting tool to cut the steel(Fe-C),the Fe atoms and C
atoms explode to everywhere.it looks like the atoms have on interaction

发自我的小米手机

Ray Shan <[email protected]…24…>编写:

how should I write the pair_coeff correctly?when I try many kind of the pair_coeff as follow ,it always wrong. the pair_coeff i have tried as follow:

pair_style hybrid eam/fs tersoff lj/cut 10.0 # lcbop
pair_coeff * * eam/fs Fe-C.eam.fs Fe C NULL NULL #Fe-C

#pair_coeff * * lcbop C.lcbop NULL C NULL NULL #C-C> #pair_coeff 1 2 lj/cut 0.00759200 3.5 9.7625 #Fe-C
pair_coeff * * tersoff BNC.tersoff NULL NULL B N #B-N
#pair_coeff 1 1 lj/cut 0.105 3.85 10 #Fe-Fe
pair_coeff 2 4 lj/cut 0.004068 3.367 #N-C
pair_coeff 2 3 lj/cut 0.003311 3.411 #B-C
pair_coeff 1 3 lj/cut 0.00284 3.4 #Fe-B
pair_coeff 1 4 lj/cut 0.00759200 3.5 9.7625 #Fe-N

EXPLORSION

What does this mean? The above commands should not generate errors. If it does not work as you expected, maybe your lj/cut parameters are not appropriate.

pair_style hybrid eam/fs tersoff lj/cut 10.0 lcbop

pair_coeff * * eam/fs Fe-C.eam.fs Fe C NULL NULL #Fe-C
pair_coeff * * lcbop C.lcbop NULL C NULL NULL #C-C
#pair_coeff 1 2 lj/cut 0.00759200 3.5 9.7625 #Fe-C

pair_coeff 3 4 tersoff BNC.tersoff NULL NULL B N #B-N
#pair_coeff 1 1 lj/cut 0.105 3.85 10 #Fe-Fe
pair_coeff 2 4 lj/cut 0.004068 3.367 #N-C
pair_coeff 2 3 lj/cut 0.003311 3.411 #B-C
pair_coeff 1 3 lj/cut 0.00284 3.4 #Fe-B
pair_coeff 1 4 lj/cut 0.00759200 3.5 9.7625 #Fe-N

ERROR:incorrect pair_coeff(tersoff)

tersoff requires “* *”

Ray

That is not a hard evidence - you certainly can’t tell a journal reviewer or your committee member that Fe and C have no interactions “because it looks like so”.

It seems to me that the problem was caused by the cutting tool.

Ray

Dear lammpser,
I was used the lammps to simulate the CBN cutting tool to cut the steel(Fe-C alloy),I uesd the eam/fs to describe the force between the Fe and C and set the CBN cutting tool as a rigid body. while I run the program for a while ,the atoms in steel will explode to everywhere, can you help me to find out the problem?

![`I9NB~_IQVBC2][email protected]…889…@M.jpg|867x565](upload://6Z71zAkeuzvOmkarBwCPsgPeIv4.jpeg)

my code is pasted below:
units metal # 单位为lammps 中的metel类型
boundary m m m # 边界条件
atom_style atomic # 原子模式
#special_bonds fene
region workpiece1 block 0 47.385 0 30 0 5 units box
region workpiece2 block 47.385 47.91 0 30 0 5 units box
region workpiece3 block 47.91 100 0 30 0 5 units box
region workpiece union 3 workpiece1 workpiece2 workpiece3 units box
region grain prism 160 180 30 65 0 5 -15 0 0 units box
#region grain cone y 127 22.5 2.5 34.50067 20 40 units box
region total union 4 workpiece1 workpiece2 workpiece3 grain units box
#建铁素体
create_box 4 total
mass 1 55.84 #Fe原子
mass 2 12.011 # C 原子
mass 3 10.811 #B原子
mass 4 14.007 #N原子

lattice custom 2.86 a1 1.0 0.0 0.0 &
a2 0.0 1.0 0.0 &
a3 0.0 0.0 1.0 &
basis 0.0 0.0 0.0 &
basis 0.5 0.5 0.5 &
basis 0.0 0.0 0.5 &
basis 0.0 0.5 0.5 &
basis 0.0 0.5 0.0 &
basis 0.5 0.0 0.0 &
basis 0.5 0.5 0.0 &
basis 0.5 0.0 0.5
create_atoms 1 region workpiece1 basis 1 1 basis 2 1 basis 3 2 basis 4 2 basis 5 2 basis 6 2 basis
7 2 basis 8 2 units box
#建奥氏体
lattice custom 3.58 a1 1.0 0.0 0.0 &
a2 0.0 1.0 0.0 &
a3 0.0 0.0 1.0 &
basis 0.0 0.0 0.0 &
basis 0.5 0.5 0.5 &
basis 0.0 0.0 0.5 &
basis 0.0 0.5 0.5 &
basis 0.0 0.5 0.0 &
basis 0.5 0.0 0.0 &
basis 0.5 0.5 0.0 &
basis 0.5 0.0 0.5
create_atoms 1 region workpiece2 basis 1 1 basis 2 2 basis 3 2 basis 4 1 basis 5 2 basis 6 2 basis
7 1 basis 8 1 units box
#建马氏体
lattice custom 3.018 a1 0.943 0.0 0.0 &
a2 0.0 0.943 0.0 &
a3 0.0 0.0 1 &
basis 0.0 0.0 0.0 &
basis 0.5 0.5 0.5 &
basis 0.0 0.0 0.5 &
basis 0.0 0.5 0.5 &
basis 0.0 0.5 0.0 &
basis 0.5 0.0 0.0 &
basis 0.5 0.5 0.0 &
basis 0.5 0.0 0.5
create_atoms 1 region workpiece3 basis 1 1 basis 2 1 basis 3 2 basis 4 2 basis 5 2 basis 6 2 basis
7 2 basis 8 2

lattice diamond 3.615 #CBN砂轮
create_atoms 3 region grain basis 1 4 basis 2 4 basis 3 4 basis 4 4 basis 5 3 basis 6 3 basis 7 3
basis 8 3 units box
group grain region grain
pair_style hybrid lj/cut 10.0 eam/fs # lcbop tersoff
pair_coeff * * eam/fs Fe-C.eam.fs Fe C C C #Fe-C
#pair_coeff * * lcbop C.lcbop NULL C NULL NULL #C-C
#pair_coeff 3 4 lj/cut 0.00759200 3.5 9.7625 #Fe-C
#pair_coeff * * tersoff BNC.tersoff B C B N #B-N
#pair_coeff 1 1 lj/cut 0.105 3.85 10 #Fe-Fe
pair_coeff 2 4 lj/cut 0.004068 3.367 #N-C
pair_coeff 2 3 lj/cut 0.003311 3.411 #B-C
#pair_coeff 1 2 lj/cut 0.003660 3.39#B-C和N-C
pair_coeff 1 3 lj/cut 0.00759200 3.5 9.7625 #Fe-B
pair_coeff 1 4 lj/cut 0.00759200 3.5 9.7625 #Fe-N
neighbor 6 bin
neigh_modify every 1 delay 5 check yes
#bond_style harmonic
#bond_coeff 1 80.0 2.0

region 1 block 5 100 5 30 0 5 units box
region 2 block 10 100 10 30 0 5 units box
group 1 region 1
group 2 region 2
group workpiece region workpiece
group boundary subtract workpiece 1
group hengwen subtract 1 2
group newton subtract workpiece boundary hengwen
group workpiece union newton hengwen
min_style sd # 能量最小化模式,sd
minimize 1.0e-15 1.0e-18 20000 20000 # 能量最小化参数,指数越大最小化程度越深
#write_restart restart.txt
compute 3 all pe/atom # 计算每个原子的势能
compute 4 all ke/atom # 计算每个原子的动能
compute 5 all coord/atom 3.0 # 计算每个原子的近邻原子数
compute temperature2 hengwen temp
compute temperature3 newton temp/region 2

compute p all pressure thermo_temp # 计算应力,计算结果记为p
variable pressx equal c_p[1] #定义变量pressx=c_p[1],c_p[1]的意思是p里第一个值
variable pressy equal c_p[2] #定义变量pressy=c_p[2],c_p[2]的意思是p里第二个值

compute m workpiece stress/atom # 计算工件应力,计算结果记为p
compute n workpiece reduce sum c_m[1] c_m[2] c_m[3]
variable px equal -(c_n[1])/(3vol)
variable py equal -(c_n[2])/(3
vol)
compute k grain stress/atom # 计算磨粒应力,计算结果记为p
compute g grain reduce sum c_k[1] c_k[2] c_k[3]
variable pgx equal -(c_g[1])/(3vol)
variable pgy equal -(c_g[2])/(3
vol)
velocity boundary set 0.0 0.0 0.0
velocity hengwen create 293.0 5812775 temp temperature2 units box
velocity newton create 293.0 5812775 units box
fix 3 all nve
fix 4 boundary setforce 0.0 0.0 0.0
fix 5 hengwen temp/rescale 10 293.0 293.0 10.0 1.0
fix 6 grain setforce 0.0 0.0 0.0
compute force grain group/group newton
fix 7 grain move linear -1.4 0 0.0 units box # tan=0.025Vw/Vs
dump result all custom 100 dump.*.lammpstrj id type mass x y z xs ys zs c_3 c_4 c_5
#dump result workpiece cfg 100 *.cfg id type xs ys zs x y z
thermo 100
thermo_style custom step c_temperature3 c_force[1] c_force[2] c_force[3] etotal press v_pressx
v_pressy v_px v_py v_pgx v_pgy
timestep 0.001 # 步长 0.001fs
run 21429 # 运行 100 步

best regards

Yao

College of Mechanical Engineering, Donghua University

Room 3034, academy building 4, 2999 North Renmin Road, Songjiang District

Shanghai, 201620, China

Tel: 86-159-0160-8286

Email: [email protected]…8…

College of Mechanical Engineering, Donghua University

Room 3034, academy building 4, 2999 North Renmin Road, Songjiang District

Shanghai, 201620, China

Tel: 86-159-0160-8286

Email: [email protected]…8…

![`I9NB~_IQVBC2][email protected]…889…@M.jpg|940x612](upload://6Z71zAkeuzvOmkarBwCPsgPeIv4.jpeg)

Is your steel stable without being cut? Have you minimized/equilibrated the steel before cutting it? What is the velocity of your cutting tool?

Ray

yes ,the cutting tool is still far from the steel,while the atoms already move to everywhere.I have minimized/equilibrated the steel before cutting ,but it still doesn’t work. the velocity of the cutting tool is 140m/s

College of Mechanical Engineering, Donghua University

Room 3034, academy building 4, 2999 North Renmin Road, Songjiang District

Shanghai, 201620, China

Tel: 86-159-0160-8286

Email: [email protected]…8…

if the steel is stable while cutting tool move thousands of step, then the steel while explode

College of Mechanical Engineering, Donghua University

Room 3034, academy building 4, 2999 North Renmin Road, Songjiang District

Shanghai, 201620, China

Tel: 86-159-0160-8286

Email: [email protected]…8…

No, you only minimized the Fe-C but not equilibrated. It is obvious that you have a bad structure and/or bad potential. I suggest you create a very simple input script from your over-complicated one that does only minimization and equilibration, then you have definite proof if your structure/potential are good.

Ray

But your steel is not stable, and I don’t know what “move thousands of step” means.

Ray