Skip to content

Latest commit

 

History

History
73 lines (63 loc) · 3.24 KB

input-kpt.md

File metadata and controls

73 lines (63 loc) · 3.24 KB

KPT file

ABACUS uses periodic boundary conditions for both crystals and finite systems. For isolated systems, such as atoms, molecules, clusters, etc., one uses the so-called supercell model. Lattice vectors of the supercell are set in the STRU file. For the input k-point (KPT) file, the file should either contain the k-point coordinates and weights or the mesh size for creating the k-point gird. Both options are allowed in ABACUS.

Generate k-mesh automatically

To generate k-mesh automatically, it requires the input subdivisions of the Brillouin zone in each direction and the origin for the k-mesh. ABACUS uses the Monkhorst-Pack method to generate k-mesh, and the following is an example input k-point (KPT) file used in ABACUS.

K_POINTS //keyword for start
0 //total number of k-point, `0' means generate automatically
Gamma //which kind of Monkhorst-Pack method, `Gamma' or `MP'
2 2 2 0 0 0 //first three number: subdivisions along recpri. vectors
last three number: shift of the mesh

In the above example, the first line is a keyword, and it can be set as K_POINTS, or KPOINTS or just K. The second line is an integer, and its value determines how to get k-points. In this example, 0 means using Monkhorst-Pack (MP) method to generate k-points automatically.

The third line tells the input type of k-points, ‘Gamma’ or ‘MP’, different Monkhorst Pack (MP) method. Monkhorst-Pack (MP) is a method which uses the uniform k-points sampling in Brillouin-zone, while ’Gamma’ means the Γ-centered Monkhorst-Pack method. The first three numbers of the last line are integers, which give the MP k grid dimensions, and the rest three are real numbers, which give the offset of the k grid. In this example, the numbers 0 0 0 means that there is no offset, and this is the a standard 2by2by2 k grid.

back to top

Set k-points explicitly

If the user wants to set up the k-points explicitly, the input k-point file should contain the k-point coordinates and weights. An example is given as follows:

K_POINTS //keyword for start
8 //total number of k-point
Direct //`Direct' or `Cartesian' coordinate
0.0 0.0 0.0 0.125 //coordinates and weights
0.5 0.0 0.0 0.125
0.0 0.5 0.0 0.125
0.5 0.5 0.0 0.125
0.0 0.0 0.5 0.125
0.5 0.0 0.5 0.125
0.0 0.5 0.5 0.125
0.5 0.5 0.5 0.125

back to top

Band structure calculations

ABACUS uses specified high-symmetry directions of the Brillouin zone for band structure calculations. The third line of k-point file should start with ‘Line’ or ‘Line_Cartesian’ for line mode. ‘Line’ means the positions below are in Direct coordinates, while ‘Line_Cartesian’ means in Cartesian coordinates:

K_POINTS # keyword for start
6 # number of high symmetry lines
Line # line-mode
0.5 0.0 0.5 20 # X
0.0 0.0 0.0 20 # G
0.5 0.5 0.5 20 # L
0.5 0.25 0.75 20 # W
0.375 0.375 0.75 20 # K
0.0 0.0 0.0 1 # G

The fourth line and the following are special k-point coordinates and number of k-points between this special k-point and the next.

back to top