Using this command the n-th dielectric function is told to import data from a standard file specified by the 'filename' parameter.

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