In this work we elaborate on recently discovered invariance principles, according to which transport coefficients are, to a large extent, independent of the microscopic definition of the densities and currents of the conserved quantities being transported (energy, momentum, mass, charge). These invariance principles can be combined with new spectral analysis methods for the current time series to be fed into the Green-Kubo formula to obtain accurate estimates of transport coefficients from relatively short molecular dynamics simulations. In this record we collect the time series of the ab initio charge flux for a simulation of molten potassium chloride, together with the Jupyter Notebooks we employed to analyse the data and produce the figures in the related article.