# Calculating the Chern number on a 2D surface of a 3D insulator

I want to calculate the Chern number of a surface of 3D time reversal insulator. I know the 3D topological insulator was characterised by the Z2 index. And the Chern number was used characterised the 2D cases and see whether the system has non trivial edge state if it broke the time reversal symmetry. But is it possible if I want the calculate the Chern number of a specific 2D plane in Brillouin zone of a 3D structure? The reason why I ask this is because I wrote a code to calculate Chern number of specific plane in brillouin zone of a 3D tight-binding structure from Wannier90 (I used the wannier90_hr.dat file to generate the tight binding matrix and solve the eigenvector directly to calculate the chern number). Since the system is time reversal invariant. I expected that the Chern number equal to 0 in every plane of the Brillouin zone. I found some non integer non-sense result. But when I work my code in 2D model, I found it is completely correct. Every things work nicely. So I’m thinking whether my concept is wrong, whether it is non-sense to use this calculation on 2D plane of a 3D structure .