Hi @buithitham, I am a bit confused by your question. Could you please post the code you are using?
With regard to the calculation of reaction energy, you will have to be very careful to write out the correct equation since you are working with grand potentials. It is also easy to get tripped up by energy normalization here. You may want to start with a simpler example to get a feel for it. If you write out all the values for Ef and where you’re getting them that would help.
My post here might also help (it’s about formation energy calculations; remember for grand potential it’s always divided by number of atoms that are not open, e.g. everything but Li).