Using this command the n-th dielectric function is told to import data from a testfile specified by the 'filename' parameter. The file must contain a table with three columns. The first column has to contain the spectral position, followed by n and k.
The n-th dielectric function should be of type 'imported dielectric function' (which is not checked at present).
You can specify the spectral unit of the file data by setting the unit_string parameter to one of the following:
String transmitted Spectral unit used
'cm^-1^' or '1/cm' > wavenumbers
'nm' > nanometers
'|m|m' or 'micron' > microns
'eV' > electron volts
'THz' > THz