Relevant keywords

The specification of each keyword relevant to calculations of conductivity tensor and dielectric function is given below.

CDDF.start
Switch on the calculations of conductivity tensor and dielectric function when you want to perform them. The default is 'off'. In case of 'off', the calculation of conductivity tensor and dielectric function is turned off.

      CDDF.start   on         # on|off, default=off

CDDF.FWHM
Setting the full width at half maximum of conductivity and dielectric function. The default is '0.2' in eV. The Lorentian function is smeared out with the parameter.

      CDDF.FWHM    0.2        # default = 0.2 (eV)

CDDF.maximum_energy
Setting the maximum energy of optical spectra for calculations of conductivity and dielectric function. The default is '10.0' in eV. The energy range begins from 0.0 eV.

      CDDF.maximum_energy    10.0    # default = 10.0 (eV)

CDDF.additional_maximum_energy
Setting the additional energy range in the frequency domain. Although the energy range for the output of conductivity and dielectric function is specified by 'CDDF.maximum_energy', for the calculations the states beyond the energy range of the output are also taken into account, since the states beyond the energy range of the output may contribute because of the broadening of Lorentzian function. The energy range for the calculations can be controlled by a keyword 'CDDF.additional_maximum_energy'. For example, when the maximum energy is 10 eV, which is specified by 'CDDF.maximum_energy', and the additional energy range is set to 1.0 eV by 'CDDF.additional_maximum_energy', then the total energy range becomes 11.0 (10.0+1.0) eV. The default value is 0.0 eV.

      CDDF.additional_maximum_energy        1.0    # default = 0.0 eV

CDDF.frequency.grid.total_number
Setting the total number of grids for conductivity and dielectric function. The default number of grids is '10000'. And, the interval in the energy grid is given by ( Maximum energy - 0.0 ) / total number of energy-grid, e.g. $( 10.0 - 0.0 ) / 10000 = 0.0010 $ (eV).

      CDDF.frequency.grid.total_number    10000    # default = 10000

CDDF.Kgrid
Setting a set of numbers (n1,n2,n3) of grids to discretize the first Brillouin zone in the k-space, which is used for the calculations of conductivity and dielectric function. For the reciprocal vectors ${\bf\tilde{a}}$, ${\bf\tilde{b}}$, and ${\bf\tilde{c}}$ in the k-space, please provide a set of numbers (n1,n2,n3) of grids as 'n1 n2 n3'. According to the (n1,n2,n3), a regular mesh in the first Brillouin zone will be generated. It does not need to be the same as scf.Kgrid which is used for the SCF calculation. So, one may use a rather coarse grid for the SCF calculation, and change to a finer grid for the calculations of conductivity and dielectric function to reduce the computational cost.

CDDF.material_type
Setting the type of material: metal or insulator. 0 is for insulator, and 1 is for insulator and metal.

      CDDF.material_type 0    # Default=0



Figure 81: The dielectric function of Si crystal (primitive cell, 2 atoms) with 6 different K-grids: $10\times 10\times 10$, $20\times 20\times 20$, $30\times 30\times 30$, $50\times 50\times 50$, $75\times 75\times 75$, and $100\times 100\times 100$. The blue and red lines are real and imaginary parts of dielectric function, respectively, where CDDF.FWHM=0.2 eV was used.
\includegraphics[width=17.0cm]{CDDF-Fig2.eps}