Book Image

Quantum Chemistry and Computing for the Curious

By : Keeper L. Sharkey, Alain Chancé
Book Image

Quantum Chemistry and Computing for the Curious

By: Keeper L. Sharkey, Alain Chancé

Overview of this book

Explore quantum chemical concepts and the postulates of quantum mechanics in a modern fashion, with the intent to see how chemistry and computing intertwine. Along the way you’ll relate these concepts to quantum information theory and computation. We build a framework of computational tools that lead you through traditional computational methods and straight to the forefront of exciting opportunities. These opportunities will rely on achieving next-generation accuracy by going further than the standard approximations such as beyond Born-Oppenheimer calculations. Discover how leveraging quantum chemistry and computing is a key enabler for overcoming major challenges in the broader chemical industry. The skills that you will learn can be utilized to solve new-age business needs that specifically hinge on quantum chemistry
Table of Contents (14 chapters)
Chapter 8: References
Chapter 9:Glossary
Appendix B: Leveraging Jupyter Notebooks on the Cloud
Appendix C: Trademarks

5.2. Example chemical calculations

As discussed in Chapter 4, Molecular Hamiltonians, approximating the PES of nuclear motion occurs due to the use of the BO approximation. We can use a semi-empirical method of approximating the PES through experimental data and/or computer simulations.

The PES can be compared to a landscape with mountains and valleys. In practice, as chemists, we want to find the global minimum (ocean floor) not local minima (mountain meadows) of the PES, as seen in Figure 5.1. We use the variational method, both classical and quantum, to find the global minimum. This can be compared to a ball rolling around the landscape. If we give the ball a nudge in some direction, generally downward, the ball will wind up in the minimum. We call this gradient descent. The gradient descent can be supplied by numerically changing input values or by an analytic formula of the wave function that describes the PES.

To state that calculation of determining the PES we guess a...