# Volume VI — Reactions and Free Energy

Chemistry is change, and change has a cost: the **activation barrier** a reaction must
climb, and the **free-energy landscape** that decides which products form and how fast.
These notebooks follow the course's calculations of reacting systems, from the
energy profile of a single bond-breaking step, through the nudged-elastic-band search
for a transition state, to metadynamics reconstructing a free-energy surface from a
biased trajectory. The energies are the course's own committed density-functional and
tight-binding results.

```{admonition} Source lectures
:class: note
This volume develops **Lecture 7** of *Molecular and Materials Modelling*
(FS 2023) — *density functionals and basis sets, on the ethanol dehydration* —
and **Lecture 13** — *transition states and free energy: the nudged elastic band
and metadynamics*. Each notebook repeats its specific lecture provenance in its
overview; the full lecture map is in `manifest.yml`.
```

```{tableofcontents}
```