Using VCA method for 2 different occupancy ratios

[mtardieux]

Dear VASP users,

I have a question concerning the Virtual Crystal Approximation (VCA) method.

In the explanation provided on the Wiki page, VCA is demonstrated with a two-atom cell to simulate Sn doping in a Ge lattice. I was wondering how this approach would work in cases where we want to mix two sites with different occupancy ratios (to introduce disorder on two different sites with different occupancies).

Let me describe my specific scenario:

I have a POSCAR file consisting of three atomic species: A, B, and C. Species A has an occupancy of 1, so if I understand correctly, the VCA parameter would be set as: VCA = 1.0 …. ….

However, for the sites occupied by B, I would like a composition of 65% B and 35% C.
On the sites initially occupied by C, I would like to adjust the composition to 15% B and 85% C.

Does anyone know how to set this within VCA?

Best,

Marie

[jonathan_lahnsteiner2]

Dear Marie,

I think the tag INCAR you are looking for is VCAIMAGES. In this way you will have to prepare two simulation folders called 01 and 02. The folder 01 should contain the pure AB and the simulation folder 02 should contain the pure AC composition. Now you can set VCAIMAGES to some real value and get the partial occupancies you are aiming for. For more information please check the wiki page.

All the best Jonathan