About phase diagram under different atomsphere

Alloy Theoretic Automated Toolkit (ATAT)
1

hi, prof. Axel van de Walle
I have some questions about several basic theories:

  1. Can ATAT calculate the phase diagram under different atomsphere? I think we can use the chemical potential to represent the atomsphere? Can ATAT do that?
  2. As I mentioned in question 1, is that the atomsphere chemical potential the same as the chemical potential in grand carnonical MC in ATAT?
  3. If we want to calculate an element chemical potential, we must find a balanced reaction I think. But in actual atomsphere, there may not be a balanced reaction, so is there any other methods to calculate the element chemical potential?

Thank you so much
liu

2

You can just run each ab initio calculation at the desired pressure ( use the PSTRESS tag if using vasp)
Otherwise, the procedure is the same.
If you want to be able to vary pressure, then that’s a bit more involved. The -P option of fitfc could help.

3

hi, avdw
Thank you for your reply. What I mean is different atmosphere, not different pressure.
Maybe 10Mpa CO or 10Mpa O2. It will influence the chemical potential I think. So is it different from ATAT used chemical potential in GCMC?

4

I see. Indeed the atmosphere sets the chemical potentials. (There is no correction needed when constructing the cluster expansion, only during the MC runs.)
The easiest way to do this is to use one point where the experimental phase boundary is known, to find the unknown reference constant in:

mu_ATAT = constant + kT ln (partial pressure)