An example of calculating the energy band structure of the topological insulator Bi\(_2\)Se\(_3\) is provided in the folder examples/Bi2Se3.

The Input file is:

    nspin                          4
    package                        ABACUS
    fermi_energy                   9.557219691497478
    fermi_energy_unit              eV
    HR_route                       data-HR-sparse_SPIN0.csr
    SR_route                       data-SR-sparse_SPIN0.csr
    rR_route                       data-rR-sparse.csr
    HR_unit                        Ry
    rR_unit                        Bohr
    max_kpoint_num                 8000

    lattice_constant               1.8897162
    lattice_constant_unit          Bohr
    -2.069  -3.583614  0.000000
     2.069  -3.583614  0.000000
     0.000   2.389075  9.546667

    wf_collect                     0
    kpoint_mode                    line
    kpoint_num                     5
    0.00000 0.00000 0.0000 100  # G
    0.00000 0.00000 0.5000 100  # Z
    0.50000 0.50000 0.0000 100  # F
    0.00000 0.00000 0.0000 100  # G
    0.50000 0.00000 0.0000 1    # L

wf_collect: Whether to output wave function matrix information. The wave function file stores the expansion coefficients of NAOs.

There are three ways to set k-points: k-point, k-line, and k-mesh, with the keyword kpoint_mode used to define the mode. The setting parameters for each mode differ, so please refer to the INPUT for detailed instructions. In this example, the line mode is used. In this mode, kpoint_num specifies the number of high-symmetry points, and high_symmetry_kpoint records the direct coordinates of these points and the number of k-points between each pair of high-symmetry points. Each row in the setting consists of four numbers, where the first three indicate the coordinates, and the last number specifies the number of k-points between the given k-point and the next high symmetry point.

After the calculation is done, a number of files will be generated in the Out/Band_Structure folder, including kpt.dat and band.dat. If kpoint_mode is set to line, the output will also include the energy band diagram and its corresponding drawing script.