KP-menu

The corresponding menu for the $\mathbf{k}$-points (KP-menu) looks like this:

/-------------------------\\

|................. K-point menu ..................|

\\-------------------------/

0. BULK calculation

NEW reciprocal lattice vectors (up to 2*PI):

BJ0(1): 0.09190 0.00000 0.00000

BJ0(2): 0.00000 0.09190 0.00000

BJ0(3): 0.00000 0.00000 0.09190

1. DOS

2. BAND: eigenvalues along a k-direction

3. Self-consistent (ordinary) calculation

Q. Return to the main menu

Specify the character and press ENTER ---->

The option 0 allows one to choose between bulk and slab calculation. It is assumed here that the vacuum gap between slabs runs along the third lattice vector $\mathbf{a}_{3}$. Although this vector may not be very large in actual calculation, in most cases related to the reciprocal space, it is convenient to assume that it is of an infinite length. This in turn implies that the Brillouin zone (BZ) in the case of a slab calculations is effectively 2D (planar, compressed in the third dimension). Thus, any $\mathbf{k}$-point to be constructed in this menu will have its component along the third reciprocal vector $\mathbf{b}_{3}$ (the reciprocal and direct primitive translation vectors are related via $\mathbf{a}_{i}\mathbf{b}_{j}=2\pi\delta_{i,j}$) removed, i.e. only $\mathbf{b}_{1}$ and $\mathbf{b}_{2}$ will be used.

Other options of the menu allows youto choose the $\mathbf{k}$-points depending on the type of the DFT calculation to be performed:

• 1 - the most sophisticated option, it allows one to use the point symmetry of the system and split the BZ into many tetrahedra for the calculation of the electronic DOS. This is specifically described in the coming Sections below
• 2 - $\mathbf{k}$-points along a direction in the BZ can be chosen; this is useful for a band-structure calculation, when dispersion curves, $\varepsilon_{n}(\mathbf{k})$, for each electronic band $n$ are to be calculated
• 3 - $\mathbf{k}$-points for a self-consistent calculation are chosen using the Monchorst-Pack method (either two or three integers to be given in the 2D and 3D cases, respectively); only inversion is assumed in this case (i.e. the points $\mathbf{k}$ and $-\mathbf{k}$ are assumed to be equivalent)

Once $\mathbf{k}$-points have been selected, a new option S appears (save, Section 2.6.11.1) that allows you to save the geometry and the $\mathbf{k}$-points. This is ok for SIESTA since everything is contained in a single input file. However, it is a little inconvenient in the case of VASP since the $\mathbf{k}$-points are always assumed to be in a different KPOINTS file (so that geometry may be saved more than once).