# TDELF in chemical reactions

With Octopus, you can perform ab initio Molecular Dynamics (MD). The model is the following: the electronic subsystem is described with TDDFT, and its density is described thanks to the Kohn-Sham system that evolves following the time-dependent Kohn-Sham (TDKS) equations. These equations include the potential exerted by the set of moving nuclei. The nuclei, in turn, are described classically, and evolve following the usual Newtonian equations. The force term includes the electronic influence by making use of the Ehrenfest theorem. In consequence, the trajectory is the "Ehrenfest path". The electronic subsystem may populate any state, excited or not, and the coupling with the nuclei includes, to a certain (not very clear) degree, non-adiabatic terms.

This framework can be used to study chemical reactions, photo-induced dynamics of molecules, or a combination of both (photo-induced chemical reactions). In this page we provide a few, visually appealing, examples of this kind of applications.

In addition to looking at the nuclear position, it is interesting to look at the electronic structure as it evolves in time (bonds break, bonds form, charge flies away and the system ionizes, etc). The time-dependent electron localization function (TDELF) is a remarkable tool tailored for this particular purpose.

## Combustion of acetylene I

${\textrm C}_2{\textrm H}_2 + {\textrm O}_2 \to 2{\textrm C}{\textrm O} + 2{\textrm H}$ ==

This first example displays the collision of the acetylene and the Oxygen molecules (i.e., the combustion of acetylene).