Suggest small change to wording on optical conductivity tutorial
The optical conductivity tutorial here: https://www.octopus-code.org/documentation//main/tutorial/periodic_systems/optical_spectra_of_solids/?series=time-dependent
gives a specific equation needed to get the correct normalization when using the delta-kick approach. This equation involves a normalization factor computable from V
(the volume of the unit cell in atomic units), the magnitude E_{0}
of the field kick in atomic units of electric field, and a factor '\omega
' in the denominator.
In the td.current\conductivity file, the header lines state that the first column is energy in atomic units (H). Are these values intended to be the needed factor \omega
for the normalization? I think this needs to be rephrased so that the meaning is slightly clearer. In atomic units, the numerical values for excitation frequencies and energies are identical. Given that the symbol \omega
is often used to denote frequency, I think that the description of the factors used for normalization should also explicitly say that this quantity \omega
is specifically the same value as the energy in atomic units.
Then the desired scaling factor changes for each line of td.general\conductivity, as the energy \omega
changes, causing a divergence if \omega = 0
.