Fe-30%Cu alloy structure mechanical properties

LAMMPS LAMMPS Beginners
1

I have to simulate Fe-Cu nano wire for different size and different temperature. I made a code but it is giving very high ultimate stress than usual. How can I generate the crystal structure? my code is:

# ------------------------ INITIATION -------------------------------- 
units metal 
dimension 3 
boundary p p p 
atom_style atomic 
variable latparam equal 2.855 #using lattice constant of Fe 
# ----------------------- Geometry of Material ----------------------- 
lattice bcc ${latparam} 
region whole block 0 25 0 25 0 25 
create_box 3 whole 
lattice bcc ${latparam} orient x 1 0 0 orient y 0 1 0 orient z 0 0 1 
create_atoms 1 region whole 
set group all type/fraction 2  0.3 93432 #making FeCu structure 
mass 1 55.845 #Fe 
mass 2 63.546 #Cu
# --------------------Potential function-------------------------------- 
pair_style meam
pair_coeff * * library.meam Fe Cu FeCu.meam Fe Cu Fe
#--------------------Equilibration-------------------------------------- 
compute csym all centro/atom fcc 
compute peratom all pe/atom 
reset_timestep 0 
timestep 0.001 
velocity all create 300 12345 mom yes rot no 
fix 1 all npt temp 300 300 0.1 iso 0 0 1 drag 1 
minimize 1.0e-4 1.0e-6 100 1000 
thermo 100 
thermo_style custom step lx ly lz press pxx pyy pzz pe temp 
run 10000 
unfix 1 
variable tmp equal "lx" 
variable L0 equal ${tmp} 
print "Initial Length, L0: ${L0}" 
#---------------------Stress-Strain Calculation---------------- 
reset_timestep 0 
fix 1 all npt temp 300 300 1 y 0 0 1 z 0 0 1 drag 1 
variable srate equal 1.0e11
variable srate1 equal "v_srate / 1.0e12" 
fix 2 all deform 1 x erate ${srate1} units box remap x 
variable strain equal "(lx - v_L0)/v_L0" 
variable p1 equal "v_strain" 
variable p2 equal "-pxx/10000" 
variable p3 equal "-pyy/10000" 
variable p4 equal "-pzz/10000" 
fix def1 all print 100 "${p1} ${p2} ${p3} ${p4}" file Fe30Cu.txt screen no 
dump 1 all custom 250 *.dump type x y z 
thermo 100 
thermo_style custom step v_strain temp v_p2 v_p3 v_p4 ke pe press 
run 40000 
#---------------------simulation completely done------------ 
print "Simulation completed"

potentia file: saved as FeCu.meam

rc = 4.0
delr = 0.1
augt1 = 0
erose_form = 2
ialloy = 2

zbl(1,1) = 0
nn2(1,1) = 1
rho0(1) = 1.000
Ec(1,1) = 4.290
re(1,1) = 2.4800
alpha(1,1) = 5.15716154
repuls(1,1) = 0.05
attrac(1,1) = 0.05
Cmin(1,1,1) = 0.36
Cmax(1,1,1) = 2.80

zbl(2,2) = 0
nn2(2,2) = 1
rho0(2) = 1.000
Ec(2,2) = 3.540
re(2,2) = 2.5550
alpha(2,2) = 5.15483008
repuls(2,2) = 0.05
attrac(2,2) = 0.05
Cmin(2,2,2) = 1.21
Cmax(2,2,2) = 2.80

zbl(1,2) = 0
nn2(1,2) = 1
lattce(1,2) =	'l12'
Ec(1,2) =	3.9445
re(1,2) =	2.57000
alpha(1,2) =	5.31447012
repuls(1,2) =	0.0500
attrac(1,2) =	0.0500
Cmin(1,1,2) =	0.36
Cmin(2,2,1) =	1.21
Cmin(1,2,1) =	0.722500
Cmin(2,1,1) =	0.722500
Cmin(1,2,2) =	0.722500
Cmin(2,1,2) =	0.722500
Cmax(1,1,2) =	2.80
Cmax(2,2,1) =	2.80
Cmax(1,2,1) =	2.80
Cmax(2,1,1) =	2.80
Cmax(1,2,2) =	2.80
Cmax(2,1,2) =	2.80

library.meam file:

#elt	lat	z	iel	atwt
#		alpha		b0	b1	b2	b3		alat	esub	asub
#		t0	t1	t2	t3	rhozero	ibar
'Fe'	'bcc'  8	1	55.8470
		5.1571615396	4.150	1.000	1.000	1.000	2.8636573352	4.290	0.560
		1.00	2.600	1.800	-7.200	1.000	3
'Cu'	'fcc'  12	1	63.5460
		5.1548300830	3.830	2.200	6.000	2.200	3.6133156519	3.540	0.940
		1.00	2.720	3.040	1.950	1.000	3
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2

This is a question about how to do your research and not about LAMMPS itself. That makes this off-topic for this forum and rather a topic for discussion with your adviser/tutor/mentor/colleagues that know and care about your research.

As far as LAMMPS is concerned, it will just take your input and apply it according to what is written in the documentation and what the selected parameters and settings determine. LAMMPS does not care whether that is meaningful or not suitable for your specific calculation. Since LAMMPS uses empirical potentials, you always have to carefully check whether your choices are suitable for the specific conditions that you are trying to implement and whether your workflow is capable of yielding consistent results for that purpose. LAMMPS will just try to do what you tell it to and only error out when either you are not following the syntax correctly or your input cannot be run in a stable way.

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3

Can you please just tell me what is the difference between following two command
pair_coeff * * library.meam Fe Cu FeCu.meam Fe Cu Fe
pair_coeff * * library.meam Fe Cu FeCu.meam Fe Fe Cu
how it affacts?

4

That question was already answered here: Pair_coeff command problem - #2 by simongravelle

1 Like
5

Where does this 3 come from? I have only 2 element Fe and Cu

6

From your input.

You have set up a system with 3 atom types.

Element != atom type

1 Like
7 
fix     1 all npt temp ${T} ${T} .008 iso 1 1 50 drag 0.5

fix 1 all npt temp 300 300 1 y 0 0 1 z 0 0 1 drag 1

What is meant by iso 1 1 50 and how does this above two command be different? what if I put 1 instead 50?