NiTi eam potential

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1

Dear Lammps users, I want to work on the tensile test of NiTi but I have problem finding the NiTi eam potential, where and how can I get the potential?

thanks in advance

2

There is one file of that kind attached here:
http://lammps.sandia.gov/threads/msg02272.html

I have no clue if that is good or not. Always better to contact the original authors if you want to be 100% the file is a good one.

Moreover, about time for you to improve your search capabilities online.

Carlos

3

How about "the literature"? Is anything published about Ni-Ti EAM?
Otherwise www.ctcms.nist.gov/~cbecker is a good place to look for EAM
potential files. Unfortunately NIST (and its website) is currently
shut down (along with the rest of the US government).

4

Dear Carlos, thank you for the reply, I had find the potential that you sent the link for me, but I think its defective because the atoms cannot be relaxed using this potential

Dear Daniel, thank you for your reply, actually there are several papers that have used NiTi eam potential and even have revealed the potential’s parameters but yet I have not been able to decipher the format of eam/fs potential file to tabulate the data from the given equations.

But I have find a potential from a website (http://atomistics.osu.edu/eam-potential-generator/index.php) generating potentials for alloys from the available elemental potentials, although I managed to relax the structure using this potential but to further verify it I obtained its cohesive energy using the following codes (This code is obtained form the tutorial: https://icme.hpc.msstate.edu/mediawiki/index.php/LAMMPS_tutorials)

The calculated cohesive energy is: -4.768 ev while the reported value of cohesive energy is -5.176 in the papers.
Does it mean that my potential is wrong??

thank you in advance

dimension 3
boundary p p p
units metal
neighbor 2 nsq
neigh_modify every 1 delay 0 check yes

#GEOMETERY
read_data inputi.txt

#POTENTIAL
pair_style eam/fs
pair_coeff * * NiTi.setfl.fs Ti Ni

#RELAXATION

---------- Define Settings ---------------------

compute eng all pe/atom
compute eatoms all reduce sum c_eng

---------- Run Minimization ---------------------

reset_timestep 0
fix 1 all box/relax iso 0.0 vmax 0.001
thermo 10
thermo_style custom step pe lx ly lz press pxx pyy pzz c_eatoms
min_style cg
minimize 1e-25 1e-25 5000 10000

variable natoms equal “count(all)”
variable teng equal “c_eatoms”
variable length equal “lx”
variable ecoh equal “v_teng/v_natoms”

print “Total energy (eV) = {teng};" print "Number of atoms = {natoms};”
print “Lattice constant (Angstoms) = {length};" print "Cohesive energy (eV) = {ecoh};”

5

To test your cohesive energy procedure take another EAM potential that comes with lammps and make sure you can reproduce the correct value. Fe is a good material to run such a test. That will help you figure out if the problems are related to the potential or to your calculation strategy.
Carlos

6

Thank you for the reply,the procedure gives the correct result for the case of Al, so I think the problem is due to my potential.
Another question, does eam potentials capture the bond breakage and formation of the system? In other word, can someone obtain the fracture stress and strain of the system using eam potentials?

7

Thank you for the reply,the procedure gives the correct result for the case of Al, so I think the problem is due to my potential.

Maybe, maybe not. You could still be making a mistake somewhere such as only allowing isotropic box relaxation when the system is trying to change the lattice ratio values to further minimize its energy.

Another question, does eam potentials capture the bond breakage and formation of the system? In other word, can someone obtain the fracture stress and strain of the system using eam potentials?

Sure they do.
Carlos