Large Basis Sets, Dissociation Energy and Geometry Optimisation

3. Large Basis Sets, Dissociation Energy and Geometry Optimisation#

Albeit deceptively small and simple, the H\(_2\) molecule with its two protons and two electrons is already too big to derive an analytic solution of the Schrödinger equation. However, one may construct a special basis set that is arbitrarily close to the complete basis set limit, and then run a post-Hartree Fock calculation. Using such techniques, it was found that, for the H\(_2\) molecule, \(E_{exact} = -1.174474{}\) a.u.

In this set of exercises, you will compare the influence of basis sets on the energy of H\(_2\) at equilibrium distance, and you will then go on to compute the dissociation energy of H\(_2\) using Hartree Fock.

Subsequently, you will determine the equilibrium geometry of a species using the example of water.

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🎯 Learning goals

Influence of basis sets

Geometry optimization procedure

Basics of HF theory: RHF vs UHF

📖 Chapter in script

Chapter 3 - Basis functions in quantum chemistry

Chapter 4 - An introduction to Hartree Fock theory

📚 Resources

Jensen, F. (2017). Introduction to computational chemistry. John wiley & sons.

  • Chapter 5 - Basis Sets

Introduction to Hartree-Fock Molecular Orbital Theory by the Sherrill group: slides and videos (part 1, part 2)

Geometry Optimization by the Sherrill group: slides and video