3. Settings
KITE uses the classes kite.Configuration
and kite.Calculation
to define the calculation settings.
This is what a typical kite.Configuration
object (for a 2D lattice) looks like:
kite.Configuration
object.
Info
The current syntax assumes that the user will simulate a 2D or 3D system as a default. However, 1D lattices can be easily constructed by simulating a strip geometry with open boundary conditions in the transverse (y) direction and ly, ny = 1
.
Divisions¶
- The
divisions
is an integer number that defines the number of decomposition parts in each spatial direction. KITEx implements an efficient domain decomposition technique to divide the lattice into various partitions that are computed in parallel. KITEx decomposition algorithms are optimized at the design level to deliver optimal multithreading scaling. Their usage for large-scale simulations is highly recommended. - To activate this feature, set a number of decomposition parts larger than one, i.e.
nx * ny > 1
(2D) ornx * ny * nz > 1
(3D).Warning
The product
nx * ny (* nz)
equals the number of threads used by KITEx and thus must not exceed the number of available cores in the compute node.
Length¶
-
The
length
is an integer number of unit cells along the direction of lattice vectors (for example,lx, ly, lz = 256, 256, 256
). The lateral size of the decomposed parts are given bylx/nx
,ly/ny
andlz/nz
.Warning
The lateral sizes
lx/nx
,ly/ny
,lz/nz
must be integers. -
Note that when using a 2D lattice, only
lx, ly, nx, ny
are needed.
Boundaries¶
-
KITE's default boundary conditions (BCs) are: periodic, open, and twisted. Moreover, a "random BCs" option is available, whereby statistical averages over ensembles of random vectors (or disorder configurations) are accelerated via the use of random twist angles drawn from a uniform distribution. This special option is particularly useful to simulate the infinite-size “bulk", since it efficiently eliminates finite size effects.
The
boundaries
is a string. Use'periodic'
for periodic BCs,'open'
for open BCs,'twisted'
for twisted BCs and'random'
for random BCs. In all cases, the system has the geometry of the unit cell, which is replicatedlx, ly, lz
times in the directions of the unit vectors. If twisted boundary conditions are used, the twistangles
must be provided in radians.Info
Different BCs can be used along the different directions. For example, impose open BCs along one spatial direction to build ribbons in 2D and slabs in 3D.
Twisted BC¶
For twisted BCs, the twist phase angles need to be specified by the user. This is done by means of an extra argument
' angles=[phi_x,phi_y,phi_z]'
where'phi_{x,y,z} \in [0, 2*M_PI]'
. The syntax is simple. For example, for a twist angle of pi/2.0 along both lattice directions in a 2D system, we can use:Random BC¶
Random BCs are defined using
mode = 'random'
. No extra arguments are required, but this option implicitly assumes that many random vectors (and/or disorder configurations) will be used (see Sec. Calculation). For a single system realization, this option is equivalent to a mere twisted-BC simulation with randomly chosen twist-angles alongx, y
andz
lattice directions.
Complex¶
- The
is_complex
is a boolean value. For optimization purposes, KITEx only considers and stores complex data with the settingis_complex=True
activated.is_complex=False
should be used for real symmetric Hamiltonians.
Precision¶
- The
precision
is an integer identifier for the used data type. KITEx allows users to define the precision of the calculation. Use0
for float,1
for double, and2
for long double.
Spectrum Range¶
-
The optional
spectrum_range
is an array of real values. By default, KITE executes an automated rescaling of the Hamiltonian (Sec. Documentation). Advanced users are encouraged to override this feature and specify the energy interval manually usingspectrum_range=[Emin,Emax]
, whereEmin, Emax
are the minimum, maximum energy eigenvalues.Lower/upper bounds should be used if exact energy eigenvalues of the lattice model are unknown (e.g. due to the presence of a disorder landscape); see Sec. Disorder for more information.
To manually set the energy spectrum limits, it is necessary to add an extra parameter (
spectrum_range
) to thekite.Configuration
class: