k-points tab

The k-points tab provides access to more detailed options for controlling the k-point set used in CASTEP calculations.

You can specify the Monkhorst-Pack k-point grid to use 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 CASTEP always uses this automatically under these conditions. This achieves a good grid with k-point separation at (or less than) the specified target more economically. As a consequence, such lattices may have much finer separations than requested as CASTEP excludes odd grids - even if they would have been closer to the specified separation - and takes the better even grids in preference.

Gamma point only: When selected, indicates that the density of states calculation uses a single k-point at (0,0,0).

Quality: When selected, generates the k-point grid using a k-point separation appropriate to the specified quality level. Select the desired quality level from the list. Available options are:

Coarse
Medium
Fine

The k-point separations associated with the three Quality settings depend on whether you select the Metal checkbox on the Setup tab:

Quality	k-point separation (Å^-1)
Quality	Metal selected	Metal not selected
Coarse	0.07	0.1
Medium	0.05	0.08
Fine	0.04	0.07

Separation: When selected, generates the k-point grid according to the specified k-point separation. Specify the k-point separation, in Å^-1, in the associated text box.

When you select the Separation, the Monkhorst-Pack parameters are derived to give the specified separation between neighboring grid points.

Custom grid parameters: When selected, generates the k-point grid 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 you select the Custom grid parameters option.

Display points...: Displays the number and fractional coordinates of the reciprocal space mesh points generated using the specified parameters.

The actual set of k-points used in the calculations may change if the symmetry of the system changes or if you request a DFT+U calculation.

Access methods

Menu	Modules \| CASTEP \| Calculation \| Electronic \| More... \| k-points
Toolbar	\| Calculation \| Electronic \| More... \| k-points

k-points tab

See Also: