How to build a supercell model

[kabume]

How can we build a supercell model to calculate the edge states? like below:

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AAAAABBBBB
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e.g., A is a topological non-trivial photonic cell and B is trivial, and "----" means Bloch boundary conditions.

By the way, it seems that we cannot build a rectangular lattice, such as a1=[1, 0], a2=[0, 2], an error would appear:

ERROR: AssertionError: norm(b1) ≈ norm(b2)

Thanks!