Additional periodicity data¶

Periodic
   EffectiveMass
      Enabled [True | False]
      KPointCoord float_list
      NumAbove integer
      NumBelow integer
      StepSize float
   End
   BandStructure
      Automatic [True | False]
      DeltaK float
      Enabled [True | False]
      FatBands [True | False]
      UseSymmetry [True | False]
   End
   BZPath
      Path # Non-standard block. See details.
         ...
      End
   End
   DOS
      EMax float
      EMin float
      NSteps integer
   End
   Screening
      dMadel float
      rMadel float
   End
End

Periodic

Type:	Block
Description:	Block that sets various details of the calculation only relevant for periodic systems.

EffectiveMass

Type:

Block

Description:

In a semi-conductor, the mobility of electrons and holes is related to the curvature of the bands at the top of the valence band and the bottom of the conduction band. With the effective mass option, this curvature is obtained by numerical differentiation. The estimation is done with the specified step size, and twice the specified step size, and both results are printed to give a hint on the accuracy. By far the most convenient way to use this key is without specifying any options.

Enabled

Type:	Bool
Default value:	False
Description:	In a semi-conductor, the mobility of electrons and holes is related to the curvature of the bands at the top of the valence band and the bottom of the conduction band. With the effective mass option, this curvature is obtained by numerical differentiation. The estimation is done with the specified step size, and twice the specified step size, and both results are printed to give a hint on the accuracy. By far the most convenient way to use this key is without specifying any options.

KPointCoord

Type:	Float List
Unit:	1/Bohr
Recurring:	True
Description:	Coordinate of the k-points for which you would like to compute the effective mass.

NumAbove

Type:	Integer
Default value:	1
Description:	Number of bands to take into account above the Fermi level.

NumBelow

Type:	Integer
Default value:	1
Description:	Number of bands to take into account below the Fermi level.

StepSize

Type:	Float
Default value:	0.001
Description:	Size of the step taken in reciprocal space to perform the numerical differentiation

BandStructure

Type:	Block
Description:	Options for band structure plotting. This has no effect on the calculated energy. [Warning: The band structure is only computed in case of k-space sampling, i.e. it is not computed for Gamma-only calculations (see: Periodic%KSpace).]

Automatic

Type:	Bool
Default value:	True
Description:	Generate and use the standard path through the Brillouin zone. If not, use the user defined path (set via Custom path in the GUI, or with the Periodic%BZPath keyword in the run script).

DeltaK

Type:	Float
Default value:	0.1
Unit:	1/Bohr
Description:	Step size in reciprocal space for band structure interpolation. Using a smaller number will produce smoother band curves at an increased computational time.

Enabled

Type:	Bool
Default value:	True
Description:	Whether or not to calculate the band structure.

FatBands

Type:	Bool
Default value:	True
Description:	Control the computation of the fat bands (only when the bandstructure is calculated). The fat bands are the periodic equivalent of the Mulliken population analysis. The definition of the fat bands can be found in the Band Documentation.

UseSymmetry

Type:	Bool
Default value:	True
Description:	If set, only the irreducible wedge of the Wigner-Seitz cell is sampled. If not, the whole (inversion-unique) Wigner-Seitz cell is sampled.

BZPath

Type:	Block
Description:	If [BandStructure%Automatic] is disabled, DFTB will compute the band structure for the user-defined path in the [BZPath] block. You should define the vertices of your path in fractional coordinates (with respect to the reciprocal lattice vectors) in the [Path] sub-block. If you want to make a jump in your path, you need to specify a new [Path] sub-block.

Path

Type:	Non-standard block
Recurring:	True
Description:	A section of a k space path.

DOS

Type:	Block
Description:	The subkeys of [DOS] allow to customize the calculation of the density of states.

EMax

Type:	Float
Default value:	0.75
Unit:	Hartree
Description:	Upper end of the energy interval in which the density of states is calculated.

EMin

Type:	Float
Default value:	-0.75
Unit:	Hartree
Description:	Lower end of the energy interval in which the density of states is calculated.

NSteps

Type:	Integer
Default value:	300
Description:	The number of energy intervals between [EMin] and [EMax] for which the density of states is calculated.

Screening

Type:	Block
Description:	For SCC-DFTB in periodic systems the Coulomb interaction is screened with a Fermi-Dirac like function defined as TODO S(r)=1/(exp((r-r_madel)/d_madel)+1). Screening is always enable, even if this section is absent. This section allows to change some details of the screening procedure.

dMadel

Type:	Float
Unit:	Bohr
Description:	Sets the smoothness of the screening function. The default is 1/10 of [rMadel].

rMadel

Type:	Float
Unit:	Bohr
Description:	Sets the range of the screening function. The default is 2x the norm of the longest lattice vector.