A fast and precise DFT wavelet code

K-point input parameters

A fast and precise DFT wavelet code
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This file is used to specify a set of k-points. If this file does not exist, only the Failed to parse (PNG conversion failed; check for correct installation of latex and dvipng (or dvips + gs + convert)): \Gamma

point will be used. The k-point generation relies on the ABINIT implementation. It is named input.kpt.

Example

MPgrid        # K-point sampling method                                                    
3 1 1         # No. of Monkhorst-Pack grid points                                          
1             # No. of different shifts                                                    
0.0 0. 0.0    # Shift values

Entry descriptions

All lines are mandatory. Follows a description line by line:

Method keyword

First line is a character string that specifies the method used to generate the k-point mesh:

  • auto: Automatic generation is used, based on the k-point density we wish in Fourier space, taking into account the symmetries of the system.
  • MPgrid: A Monkhorst-Pack grid, using only the special k-points, taking into account the symmetries of the system.
  • manual: A manual set of k-points.

The following lines depend on the choice of the method.

Specific parameters for method auto

One additional line containing a real space length kptrlen is required. BigDFT will automatically generate a large set of possible k-point grids, and select among this set, the grids that give a length of smallest vector LARGER than kptrlen, and among these grids, the one that, reduces to the smallest number of k-points.

Specific parameters for method MPgrid

Several additional lines are mandatory.

  • The first line should contains three integers describing the mesh of Monkhorst-Pack grid in reciprocal space.
  • The second line contains one integer nshiftk that give the number of shift one would like to apply to the MP grid to obtain the final k-point mesh.
  • Then the file contains nshiftk lines with three real numbers each, giving the shift to apply in reciprocal space.

Specific parameters for method manual

Several additional lines are mandatory.

  • The first contains nkpt, an integer giving the number of manually defined k-points.
  • Then nkpt lines follow, with four real values each, the three first being the coordinates in reciprocal space (in [0;0.5]) and the fourth being the weight. If the sum of all weights does not equal to one, weight values are renormalised.

Additional parameters for a band diagram

After the regular k-point mesh for the self-consistent loop, one can define in addition a specific path of k-points to be used to compute a band diagram. This requires also to define Davidson usage in the input.dft file. The band structure is define if the following lines are present:

  • bands keyword: a character string containing bands.
  • the next line contains one integer, nseg the number of different segments for the path.
  • the next line contains nseg integer values, defining the number different k-points to be generated in each segment. It contains also a last integer value which is the granularity, i.e. the number of k-points to be treated simultaneously in the Davidson treatment.
  • then follow nseg + 1 lines containing each three floating point values with the coordinates of the vertices in reduced coordinates of the Brillouin zone.
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