How to charge a system NiO with oxygen vacancy

[xanh]

I have a question which would like to get suggest from all you.
I follow the guide from tutorial for electronic structure of NiO using LDA . I have a NiO cell , i want take out one oxygen ion (O-2) therefore the NiO system will be charge +2 . However , I dont find out the way to charge the system to simulate the bandgap .

Could any one can help me in this issue? thank you for your help

[Anders Blom]

From a purely technical standpoint, this is obtained by adding the keyword "charge" to the LCAOCalculator(). Like so:

Code

calculator = LCAOCalculator(charge=-1)

This cannot, currently, not be done from within VNL, you have to edit the script manually. You will need to set "multipole" boundary conditions to handle a charged system. Numerically, it is often much harder to converge charged systems than neutral ones, so expect to use a lot of k-points, and perhaps a high temperature, at least to start with. As for the physics, one has to be aware that the model you compute is in reality a crystal of ions, since we don't add any background compensating charge. Therefore the best idea is probably to make a large supercell, so that the net charge is small compared to the total amount of electrons. Good luck!