Introduction to approximate quantum chemistry

Approximate quantum chemistry is a range of approaches and methods that do not aim to solve the quantum mechanical equations in a rigorous manner, but rather to use simple ideas and quantities derived from experiment to obtain insight and rough predictions of chemical quantities. The earliest method, Hückel method, was developed long before digital computers were common and all computatonal methods use few computer resources. Since in computational chemistry the resources used rise, often steeply, with the size of the molecules being studied, these methods can now be applied to very large molecules.

The material will branch out from the links below. The first two sections of this module introduce you to some of the fundamental concepts of molecular orbital (MO) theory. Sections 3 and 4 explore some practical implementations of this theory.

1. Qualitative MO theory
2. Quantitative MO theory
3. Empirical MO methods
   • Hückel method
   • Extended Hückel method
4. Semi-empirical MO methods