Chapter 6: Beyond Born-Oppenheimer

“The first principle is that you must not fool yourself – and you are the easiest person to fool.”

– Richard Feynman

“Scientific progress is measured in units of courage, not intelligence.”

– Paul Dirac

Figure 6.1 – Dr. Keeper Sharkey imagining molecular vibrations of a diatomic molecule [authors]

Determining molecular structure and vibrational spectra computationally are two essential goals of modern computational chemistry that have applications in many areas, from astrochemistry to biochemistry and climate change mitigation. The computational complexity grows exponentially when the number of atoms and/or identical particles increases linearly. There is additional complexity associated when there are significant couplings between rotational and vibrational degrees of freedom, and at high energy states, including near the dissociation and ionization limit...