We actually provide the source code for most plugins, so you can find how the spectral current is computed by inspecting the Python code of the Inelastic Transmission Spectrum Analyzer in lib/site-packages/AddOns.
You will then find this:
def plotSpectralCurrent(self):
"""
Plot spectral current vs. energy.
"""
# Get the inelastic transmission spectrum object.
its = self._model['inelastic_transmission_spectrum']
# Get data from model.
bias_point = self._model['bias_point'] * Volt
fermi_shift = self._model['fermi_shift'] * eV
temperature = self._model['temperature'] * Kelvin
phonon_modes = self._phononModes()
kpoints = self._kPoints()
qpoints = self._qPoints()
spin = self._model['spin']
# Calculate spectral current
i, i_s, energies = its.inelasticCurrentIntegral(bias=bias_point,
modes=phonon_modes,
temperature=temperature,
fermi_shift=fermi_shift,
k_indices=kpoints,
q_indices=qpoints,
spin=spin)
i_s = i_s.inUnitsOf(Ampere/eV)[0, :]
self.figure().clear()
self._axes1 = self.figure().add_subplot(111)
self._plot1 = self._axes1.plot(energies.inUnitsOf(eV), i_s, 'k-')
self._axes1.set_xlabel('Energy (eV)')
self._axes1.set_ylabel('Spectral current (A/eV)')
self.draw()
You should be able to use this in a script to get what you need. Also see https://docs.quantumatk.com/manual/Types/InelasticTransmissionSpectrum/InelasticTransmissionSpectrum.html, although it's not so clear from that page...