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Dear VASP users,

I have carefully read the wiki page on the VCA (and VCAIMAGES) tag but still have a question regarding its application.

In the tutorial, the VCA tag is used to simulate Sn doping in a Ge lattice. This is achieved using a POTCAR file with Ge and Sn datasets, a POSCAR file where the atomic positions are duplicated, and setting the VCA tag to 0.99 0.01.

How should the VCA tag be set to simulate a material of the form A1-xBxC1?
(i.e., where two atomic species are mixed, but the third species has full occupancy.)

Best regards,
Marie

Dear Marie,

In principle it is just a matter of writing

VCA = 0.99 0.01 1

and then making sure that the atoms from the species that have VCA=1 do not have replicas in the POSCAR. Please be aware that, as we explain here, this method is often not very reliable. As it is also explained on that page, you might need to generate new pseudo-potential files for elements with fractional VCA.

Kind regards,
Pedro