[Wannier] Defining projection for half-filled orbitals

[Vahid Askarpour]

Dear Wannier Community,

I am attempting to generate the Wannier functions for the valence states of Mg3As2 (semiconductor). The 8 valence states consist of Mg s-states  and As s and p states. Mg atoms have 2 electrons and As atoms have 5 for a total of 16 electrons.

The 3 Mg atoms are not equivalent. Two Mg atoms form covalent bonds with the two As atoms. The third Mg atom donates two electrons to complete the covalent bonding. So the bonding is a mixture of ionic and covalent, i.e., [Mg](+2)[Mg2As2](-2) with Mg2As2 being covalently bonded.

To generate 8 Wannier functions, I define As:s and Mg:s and get 5 states. The other 3 states have to come from As p-states. If I set As:px,py,pz then I get 6 extra states instead of 3. I could define As1:px and As2:py,pz but the As atoms are equivalent and so should be their projections I assume.

My question is how do I define three projections for the half-filled p states of the two As atoms? Or is there another way to look at this system?

I would appreciate any suggestions you might have.

Thank you,

Vahid

Vahid Askarpour
Department of Physics and Atmospheric Science
Dalhousie University,
Halifax, NS, Canada