How to calculate surface energy of alloy ?

[weizz]

Dear VASP Forum:

I want to calculate surface energies of surface alloy AuPd(100) .
My question is how to calculate the Bulk energy of alloy?


thanks !

[forsdan]

In reality if you have several coexisting phases in your system, the (local) chemical potentials should (at least in theory) be used for the energy references, since the surface energy is the change in Gibbs free energy per change in surface area. The common practice for a first approximation in surface energy calculations is nevertheless to evaluate the surface energy with respect to the pure bulk phase. This usually gives valueable and reliable information about the energy costs required to introduce the 2D defect.

The standard procedures to obtain the bulk reference are either that you perform an independent bulk calculation or that you gradually add layers to your slab until the energy difference between the thicker slab and the former thinner slab converges. Please have a look at Phys. Rev. B 49, 16798 - 16800 (1994), where the pros and cons are discussed. Then you can define the surface energy with respect to the obtained bulk reference.

However, if you have a surface system where the number of Au and Pd atoms don't add up to an integer number of bulk units, then you'll need to evaluate the chemical potentials for your specific system environment.

So it depends on your situation. I don't know which structure the AuPd alloy possesses and you haven't provided the information so I can't be more specific.

Cheers,
/Dan

<span class='smallblacktext'>[ Edited Sun Aug 16 2009, 03:44PM ]</span>

[sharma]

Can you please explain how to calculate chemical Potential of Pt and Ni. I want to calculate the surface energy of Pt3Ni(001) surface with different terminations to confirm which termination is stable. I want to use the thermodynamic method to calculate gibb's free energy.
<span class='smallblacktext'>[ Edited Mon Sep 05 2011, 05:31AM ]</span>