QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: Dhirendra on April 23, 2016, 11:10

Title: Chemical potential for the surface energy calculations
Post by: Dhirendra on April 23, 2016, 11:10

I  want to calculate the surface energies in a slab simulations. I am referring to this paper  http://dx.doi.org/10.1063/1.4761994 (http://dx.doi.org/10.1063/1.4761994) (Figure 2) which uses ATK + Thermodynamics to relate the chemical potential to the surface energy. I am confused with the use of chemical potential there. It corresponds to the Rhodium reservoir. If I simulate the Rhodium bulk in Quantumwise and calculate the chemical potential using the ChemicalPotential function, and the same for the Silicon, then is this ChemicalPotential corresponds to what paper refers to, an energy for the Rhodium reservoir?
The ChemicalPotential what ATK returns is actually a Fermi level.

Title: Re: Chemical potential for the surface energy calculations
Post by: Jess Wellendorff on April 25, 2016, 08:41

It looks like that paper uses VASP, not ATK. The chemical potential in a bulk is exactly the Fermi level. The Rhodium chemical potential in Eq. 3 is a free variable, and is defined as 0 eV in the bulk.

Title: Re: Chemical potential for the surface energy calculations
Post by: Umberto Martinez on April 25, 2016, 11:10

Regarding Schottky-barrier calculations you may want to check out our latest work where, among other things, we compare the slab approach with the device configuration and NEGF approach as implemented in ATK.
http://arxiv.org/abs/1601.04651
Phys. Rev. B 93, 155302 (2016) http://dx.doi.org/10.1103/PhysRevB.93.155302

Title: Re: Chemical potential for the surface energy calculations
Post by: Dhirendra on April 25, 2016, 12:12

Thanks Jess and Umberto,

I think the chemical potential returned by ATK is related to the electrons where as in the surface calculations one needs it for the material. So the chemical potential returned by ATK is irrelevant for the surface energy calculations. And yes the eq 3 of the paper uses it as a variable, so its not calculated from the DFT. Thanks. One of the earlier posts on the forum cleared some concepts for me.

Title: Re: Chemical potential for the surface energy calculations
Post by: Jess Wellendorff on April 26, 2016, 08:39

OK. Let me just comment on the chemical potential: It is the energy of the highest occupied electronic level, so it always has to do with electrons, no matter what material you are looking at.

Title: Re: Chemical potential for the surface energy calculations
Post by: Ulrik G. Vej-Hansen on April 26, 2016, 14:40

Just to clarify: Jess is explaining what is meant by ChemicalPotential in ATK - here it is always for the electrons. Of course you can talk about the chemical potential of other species, but there is no specific functionality to calculate that in ATK.