.. _TDDFT:

=========================
Runing TDDFT calculations
=========================

In PyNAO, time dependent density functional theory (TDDFT) is implemented in
linear response regime [koval2018pynao]_. In this section we will give a
short introduction
of the theory, then explain how to execute TDDFT calculations. In PyNAO,
two kind of excitations are possible

* the traditional light excitation which permit to calculate the polarizabilty
  of a molecule (and then its absorption)
* Electron energy loss spectroscopy, which excite the system via moving charges.
  This spectroscopy method permit to access so called dark mode.

Finally, we will show how to calculate the spatial distribution of the density
change and the induced electric field generated by such excitations [Barbry2015]_.

Theory
======

TODO

System initialization
=====================

TODO


Calculate Polarizability
========================

TODO

Calculate EELS spectra
======================

TODO

Calculate Spatial distribution of density change and induced electric field
===========================================================================

TODO