Help to use MEAM for Al2O3

Hi. Friends
I m study on Al2O3 by simulation in lammps. the Potential function is MEAM.
I want to input the “re” parameter of MEAM, for single element of O and Al in library file. but in library.meam file there is no choice to input this parameter and in AlO.meam I can just input the re(I,J) format for Al-O interaction.
I input the “re” for single element by following format to understand what should I do for this.

re(1)=value , re(2)=value format.
r(1,1)=value , r(2,2)= value format.

without the “re” for single element.

In all of 3 cases the lammps don’t show me any error and all of the answers are different from each other.

please help me how can I input the “re” for single element in MEAM potential.

Thanks

Perhaps Greg can answer this Q.

Steve

Hi. Friends
  I m study on Al2O3 by simulation in lammps. the Potential function is MEAM.
  I want to input the "re" parameter of MEAM, for single element of O and Al in library file. but in library.meam file there is no choice to input this parameter and in AlO.meam I can just input the re(I,J) format for Al-O interaction.
I input the "re" for single element by following format to understand what should I do for this.
re(1)=value , re(2)=value format.
r(1,1)=value , r(2,2)= value format.
without the "re" for single element.
In all of 3 cases the lammps don't show me any error and all of the answers are different from each other.
please help me how can I input the "re" for single element in MEAM potential.

Thanks

Hello Mohammad,

I am Bohumir, working at CAVS, Mississippi State University.

I am glad you are interested in MEAM.

You can follow our MEAM potential as an example:
  http://www.ctcms.nist.gov/potentials/Al-Si-Mg-Cu-Fe.html
Most of the MEAM results published in the accompanying article are
reproducible using ASE routines uploaded here:
   http://code.google.com/p/ase-atomistic-potential-tests/

We specify the "re" parameter for single element as "alat" in the "meamf" file.
For the cross (unlike) pairs, e.g. re(Al,O), specify re(1,2) in the
"meam.alsimgcufe".

Look into this thread for more details:
   http://lammps.sandia.gov/threads/msg31224.html

I don't think "r(1,2)" does anything. It would be good to implement
error checking for that.

It would be great to know more about your work and team.

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

Dear Bohumir
many thanks for your answer.
1- I am so apologize for write the r(1,1) instead of re(1,1).
I used the re(1,1) and re(2,2) in AlO.meam, and the lammps didn't show any error.
2- in the lammps documentation the "alat" parameter in "meamf" is different from "re". for example
the value of alat for Aluminum is 4.05 and the re is 2.86 (www.osti.gov/energycitations/servlets/purl/224267-allunm/webviewable/Modifiedembeddedatommethodcalculationsofinterfaces.pdf).
3- in my experience, the result of simulation is not depend to alat parameter. because I use different values for Oxygen and the result was quite the same.
I am very confuse about this and please help me.

Dear Mohammad,

"re" is the equilibrium nearest neighbor distance for Al
"alat" is the lattice parameter for Al

That is why they differ. Notice that 4.05/sqrt(2.0) ~= 2.86.

Likely, results of your simulations do not depend on "alat" parameter
because "re" specified in the MEAM parameter file ("AlO.meam") will
override the "alat" value from the MEAM library file ("meamf"). That
would follow the statement from
  http://lammps.sandia.gov/doc/pair_meam.html
"If used, the MEAM parameter file contains settings that override or
complement the library file settings."

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

PS: If you say a few words about yourself, people in the forum would
be more willing to answer your questions. Scientists are very curious
:slight_smile:

For a single element interaction, the "re" parameter (which is the equilibrium atomic spacing) can be set in the library file through the lattice parameter (alat). How this gets computed depends on the lattice type. For example, for an FCC crystal, re = alat/sqrt(2). For a dimer structure, which might be how you're specifying oxygen, re = alat.

Although there should be no need, if you want you can override this value by specifying something in the potential file. In that case, the correct syntax is to provide two indices, e.g. re(1,1)=value. I don't think there's any error checking done if you don't provide both indices, so the behavior may be undefined if you specify re(1)=value.

Regards,
Greg

Greg Wagner
Manager, Thermal/Fluid Science and Engineering Department
Sandia National Laboratories, Livermore, CA
Tel: (925) 294-2180 Fax: (925) 294-3410
Email: [email protected]

Dear Greg
Thanks, for your answer.
the re for Oxygen is 1.21 from Baskes article"
http://www.osti.gov/energycitations/servlets/purl/224267-allunm/webviewable/224267.pdf",
and the lattice constant for oxygen is 5.0403 from "
http://www.webelements.com/oxygen/crystal_structure.html". (in all sites
that I found from search result , the lattice constant for oxygen is ~5.403
!!!!!!.
now, as in you said that re=alat for oxygen (dimer structure), but here, I
don't know which one is correct, 1.21 or 5.043?
please let me know about this problem?
thanks

Dear Greg
Thanks, for your answer.
the re for Oxygen is 1.21 from Baskes
article"http://www.osti.gov/energycitations/servlets/purl/224267-allunm/webviewable/224267.pdf",
and the lattice constant for oxygen is 5.0403 from
"http://www.webelements.com/oxygen/crystal_structure.html". (in all sites
that I found from search result , the lattice constant for oxygen is ~5.403
!!!!!!.

you are comparing apples and oranges here.

now, as in you said that re=alat for oxygen (dimer structure), but here, I
don't know which one is correct, 1.21 or 5.043?

5.043 makes no sense in this context.
please think about it for a while...

axel.