Tutorial:Optical spectra from time-propagation

In this tutorial we will learn how to obtain the absorption spectrum of a molecule from the explicit solution of the time-dependent Kohn-Sham equations. We chose as a test case methane (CH₄).

Ground-state

Before starting out time-dependent simulations, we need to obtain the ground-state of the system. For this we use basically the same inp file as in a previous tutorial

CalculationMode = gs
Units = eV_angstrom

radius = 4
spacing = 0.175

CH = 1.2
%Coordinates
  "C" |           0 |          0 |           0 | no
  "H" |  CH/sqrt(3) | CH/sqrt(3) |  CH/sqrt(3) | no
  "H" | -CH/sqrt(3) |-CH/sqrt(3) |  CH/sqrt(3) | no
  "H" |  CH/sqrt(3) |-CH/sqrt(3) | -CH/sqrt(3) | no
  "H" | -CH/sqrt(3) | CH/sqrt(3) | -CH/sqrt(3) | no
%

After running Octopus, we will have the Kohn-Sham wave-functions of the ground-state in the directory restart/gs.