The k-points tab provides access to more detailed options for controlling the k-point set used in CASTEP calculations.
The Monkhorst-Pack k-point grid to be used in the calculation can be specified in several ways. For cubic cells and for the C direction of hexagonal cells the even and odd grids for the Monkhorst-Pack scheme give the same number of k-points. However, the even grid provides better sampling and will always be used automatically under these conditions. This ensures that a good grid with k-point separation at (or less than) the specified target can be achieved more economically. As a consequence, such lattices may have much finer separations than requested as odd grids have been excluded - even though they would have been closer to the specified separation - and the better even grids have been taken in preference.
Gamma point only: When selected, indicates that a single k-point at (0,0,0) will be used for the density of states calculation.
Quality: When selected, indicates that the k-point grid will be generated using a k-point separation appropriate to the specified quality level. Select the desired quality level from the dropdown list. Available options are:
The k-point separations associated with the three Quality settings depend on whether the Metal checkbox on the Setup tab is checked and are as follows:
|Quality||k-point separation (Å-1)|
|Metal checked||Metal unchecked|
Separation: When selected, indicates that the k-point grid will be generated according to the specified k-point separation. Specify the k-point separation, in Å-1, in the associated text box.
When the Separation option is selected, the Monkhorst-Pack parameters are derived to give the specified separation between neighboring grid points.
Custom grid parameters: When selected, indicates that the k-point grid will be generated using the Monkhorst-Pack grid parameters and the origin shift in fractional reciprocal space coordinates specified in the Grid parameters and Origin shift text boxes, respectively.
Grid parameters: Specify the Monkhorst-Pack grid parameters in each of the lattice directions.
Actual spacing: Displays the k-point separation, in Å-1, resulting from the currently specified Monkhorst-Pack grid parameters in each of the lattice directions.
Origin shift: Specify the offset of the Monkhorst-Pack grid in fractional reciprocal space coordinates.
The Grid parameters and Origin shift controls are enabled only if the Custom grid parameters option is selected.
Display points...: Displays the number and fractional coordinates of the reciprocal space mesh points that would be generated using the currently specified parameters.
The actual set of k-points that will be used in the calculations may be altered if the symmetry of the system changes or LDA+U calculation is requested.
|Menu||Modules | CASTEP | Calculation | Electronic | More... | k-points|
|Toolbar||| Calculation | Electronic | More... | k-points|
Brillouin zone sampling
Setting electronic options
Electronic tab - CASTEP Calculation dialog
Basis tab - CASTEP Electronic Options dialog
SCF tab - CASTEP Electronic Options dialog
Potentials tab - CASTEP Electronic Options dialog