MEAM potential- B1 reference structure

Dear Mohammad,

please always send a copy of your replies to the lammps mailing list.

1- please let me know where is my fault to reach the correct Ec (6.3 ev)?

Try to add bkgd_dyn = 1 to AlO.meam file and remember that 6.3 eV is expremental value,you should obtain 6.04 eV for this potential (according to Baskes).

2- I am studding on interface of Al/Al2O3, which potential is the newest and you suggest for my study?

Well, that is more difficult question because I’m not a specialist in this task. Potential by Vashishta et al. http://dx.doi.org/10.1063/1.2901171
is rather good for pure Al2O3 but I’m not sure that is applicable for the interface of Al/Al2O3

Anyway, meam potential is a good starting point due to it’s simplicity.

Grigory Smirnov

2013/2/25 mohammad sharif <mohammad.sharifzeyd@…24…>

Dear Girgory

Thanks for your reply.

I tried simulate the 600 atom of Al2O3 by bkgd_dyn = 1 and I have done it for 4000 atom.

the first level of total energy in beginning of simulation was good, but by advanced in simulation time

the total energy go on and was bigger even than 6.3. I verify the snapshut of crystal structure during

simulation and I have seen, the atoms are very disturb and seprated from crystal structure and was very bad.

I attached the pics of trend of total energy vs time in bkgd_dyn = 1 & bkgd_dyn = 0.

I don’t know, I am in correct way by bkgd_dyn = 1 or not.

I will be so happy if let me know your comments.

thanks

Mohammad

bkgd_dyn =0.png

bkgd_dyn =1.png

Dear Mohammad,

I guess your input script is incorrect. I have attached the input file that works for me. Hope it will help you.

Grigory Smirnov

al2o3.in (1.53 KB)

Dear Grigory

At first, thanks for your good input script. I have found that there is difference between my data file (Lattice structure) and that you write in input script. I think, I have to verify the boundaries of my data file that I have built by Crystalmaker and Topotools, because of the jpg snapshot show me the boundaries are very disordered during relaxation when I have defined P P P boundary.

I ran your input script in NVE ensemble and the result of E/atom was -5.98 and the snapshot of the Al2O3 structure (dump jpg) was normal. Now I have a couple of question:

1-In my data file, I have tried to make the unit cell by much software such as Avogadro, Crystalmaker by using unit cell coordination, 2 basis atom and space group but in all of it the structure disordered during relaxation. I have tried to find the reference of your Al2O3 structure but I couldn’t find it. Please let me know what is the reference of Al2O3 structure in your script?

2-When I ran your script in NVE ensemble, the E/atom will be constant after some steps and the snapshot of the lattice structure was very good, but when I ran it by NVT instead of NVE the E/atom reduce continuously and have reached to -7.4 (attached pic) and the snapshot of the structure was very disordered (attached Pic). I have used " fix 1 all nvt temp 300 300 0.001" for NVT command. I have studied in the following article that the E/atom of Al2O3 in NVT ensemble is about -6.3 (Baskes parameter). Why in the simulation by bkgd_dyn=1 and NVT ensemble the E/atom reached to -7.4 and the snapshot show the disordered in lattice structure? (I think it will reduced if I continue the simulation)

http://www.sciencedirect.com/science/article/pii/S092145260800505X

Thanks

Mohammad

NVT-pe_atom.png

NVT-Relaxed.jpg

Sorry for my late reply - I didn’t have enough time to write you email

Comments below

1 Please let me know what is the reference of Al2O3 structure in your script?

I corrected atom positions and lattice constants according to Baskes original article. May be there is an error in my input script, I need 2-3 days to check it.

  1. Why in the simulation by bkgd_dyn=1 and NVT ensemble the E/atom reached to -7.4 and the snapshot show the disordered in lattice structure?

Sorry, but I don’t know. I just made a couple of small tests for this MEAM potential and I didn’t use it for real calculations.

Grigory

Dear Grigory
1-I will glad if send me the name and web link of Baskes original article that you have wrote in your previos Email.
2-please let me know is there any technical diffrence between use ‘replicate 4 2 4’ command and ‘region 0 4 0 2 0 4 units lattice’ command to create simulation box, such as your script. Because of have some problem to use replicate for creation of big simulation box. I want to know som diffrentce exept of use minimise to minimise the total energy of unit cell befor create simulation box.
Thanks
Mohammad

Sear Grigory

I am sorry that I reply this email again. it will be very helpful if you send me

the name and web link of Baskes original article that you have wrote in your previews Email.

Thanks

I am sorry, I missed your previous message. I attached the article and the input file with correct coordinates according to this article.

I also did several test runs and found the strange effects. If the temperature is rather small, for example 50-100K, everything is ok.
But if the temperature is higher (300 K), crystal is unstable, as you mentioned in one of the previous emails. I don’t have reasonable explanation for this phenomenon.
I recommend you carefully check every parameter in meam files or try to find people who have successfully implemented this potential in lammps

Grigory

2013/3/25 mohammad sharif <mohammad.sharifzeyd@…24…>

Baskes - .pdf (5.08 MB)

al2o3.in (1.54 KB)

Hello Mohammad,

you can try "ibar = -5" together with "bkgd_dyn = 1".
For example here
  http://www.ctcms.nist.gov/potentials/Al-Si-Mg-Cu-Fe.html
we used "ibar = -5" to match results of Mike Baskes.

-Bohumir
http://www.cavs.msstate.edu/directory/information.php?eid=69

Dear Bohumir
Thanks for your reply. I used the ibar=-5 instead of ibar=3, but the results are -nan.
from page #3 of the Baskes article that I should use ibar=3.
I attached my library files that if let me know if there is any problem or you have any suggestion.
I have challenge with this problem for a long time and I will be glad if help me.
Thanks
Mohammad

Dear Bohumir
Thanks for your reply. I used the ibar=-5 instead of ibar=3, but the results are -nan.
from page #3 of the Baskes article that I should use ibar=3.
I attached my library files that if let me know if there is any problem or you have any suggestion.
I have challenge with this problem for a long time and I will be glad if help me.
Thanks

library.meam (2.8 KB)

AlO.meam (197 Bytes)

Dear Grigory
Special thanks for your helps. I have a basically question. I used some software and articles information (space group, fractional coordination and . . .) to create the Al2o3 structure. I am very interested to know how you used just the “lattice constants” and “internal coordinates” that was in the Baskes Article to create the structure.

Thanks