Chern numbers in two-dimensional systems with spiral boundary conditions

We discuss methods for calculating Chern numbers of two-dimensional lattice systems using spiral boundary conditions, which sweep all lattice sites in one-dimensional order. Specifically, we establish the one-dimensional representation of Fukui-Hatsugai-Suzuki's method, based on lattice gauge theory, and the Coh-Vanderbilt's method, which relates to electronic polarization. The essential point of this discussion is that the insertion of flux into the extended one-dimensional chain generates an effective current in the perpendicular direction. These methods are valuable not only for a unified understanding of topological physics in different dimensions but also for numerical calculations, including the density matrix renormalization group.