Optical properties

OpticalCalculation

(logical): If specified, the imaginary part of the dielectric function will be calculated and stored in a file called Systemlabel.EPSIMG. The calculation is performed using the simplest approach based on the dipolar transition matrix elements between different eigenfunctions of the self-consistent Hamiltonian. For molecules the calculation is performed using the position operator matrix elements, while for solids the calculation is carried out in the momentum space formulation. Corrections due to the non-locality of the pseudopotentials are introduced in the usual way.

Default value: false

Optical.EnergyMinimum

(real energy): This specifies the minimum of the energy range in which the frequency spectrum will be calculated.

Default value: 0 Ry.

Optical.EnergyMaximum

(real energy): This specifies the maximum of the energy range in which the frequency spectrum will be calculated.

Default value: 10 Ry.

Optical.Broaden

(real energy): If this is value is set then a Gaussian broadening will be applied to the frequency values.

Default value: 0 Ry.

Optical.Scissor

(real energy): Because of the tendency of DFT calculations to under estimate the band gap, a rigid shift of the unoccupied states, known as the scissor operator, can be added to correct the gap and thereby improve the calculated results. This shift is only applied to the optical calculation and no where else within the calculation.

Default value: 0 Ry.

Optical.NumberOfBands

(integer): This option controls the number of bands that are included in the optical property calculation. Clearly this number must be larger than the number of occupied bands and less than or equal to the number of basis functions (which determines the number of unoccupied bands available). Note, while including all the bands may be the most accurate choice this will also be the most expensive!

Default value: All bands.

Optical.Mesh

(data block): This block contains 3 numbers that determine the mesh size used for the integration across the Brillouin zone. For example:

        %block  Optical.Mesh
          5 5 5
        %endblock  Optical.Mesh

The three values represent the number of mesh points in the direction of each reciprocal lattice vector.

Default value: Empty in general. For atoms or molecules a k-sampling of only one point is assumed.

Optical.OffsetMesh

(logical): If set to true, then the mesh is offset away from the gamma point for odd numbers of points.

Default value: false

Optical.PolarizationType

(string): This option has three possible values that represent the type of polarization to be used in the calculation. The options are polarized, which implies the application of an electric field in a given direction, unpolarized, which implies the propagation of light in a given direction, and polycrystal. In the case of the first two options a direction in space must be specified for the electric field or propagation using the Optical.Vector data block.

Default value: polycrystal

Optical.Vector

(data block): This block contains 3 numbers that specify the vector direction for either the electric field or light propagation, for a polarized or unpolarized calculation, respectively. A typical block might look like:

        %block  Optical.Vector
          1.0 0.0 0.5
        %endblock  Optical.Vector

Default value: Empty.