I did a calculation on a bulk system with DFT and fit it with the tight binding matrix with wannier90. There is question on this. I try to write my own code to construct a slab tight binding matrix from this bulk matrix. But I can't find any documentation mention how the orbital basis was arrange in this matrix. (for example, I don't know which column correspond to particular orbital and particular atom.) I can only obtain the energy spectrum from it. Is there anyone who did this before ?