kabume/Qc_real_space_method

calculate multipole moments Qc by real space method, BBH model.

Calculate multipole moments by real space method

1. BBH: Qc and Px
2. SSH: Px

reference:

1. https://journals.aps.org/prb/abstract/10.1103/PhysRevB.100.245135
2. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.80.1800
3. https://topocondmat.org/w8_general/invariants.html