A Programmable K · P Hamiltonian Method and Application to Magnetic Topological Insulator MnBi2Te4

In the band theory, first-principles calculations, the tight-binding method and the effective k · p model are usually employed to investigate the electronic structure of condensed matters. The effective k·p model has a compact form with a clear physical picture, and first-principles calculations can give more accurate results. Nowadays, it has been widely recognized to combine the k ·p model and first-principles calculations to explore topological materials. However, the traditional method to derive the k · p Hamiltonian is complicated and time-consuming by hand. In this work, we independently developed a programmable algorithm to construct effective k · p Hamiltonians for condensed matters. Symmetries and orbitals are used as the input information to produce the one/two-/three-dimensional k ·p Hamiltonian in our method, and the open-source code can be directly downloaded online. At last, we also demonstrated the application to MnBi2Te4-family magnetic topological materials.