2. Optimizing molecular geometry

2.1 Principles of molecular geometry optimization

Most calculations ab initio, for example a calculation of normal modes of vibration, requires optimization of the geometry (or structure) of a molecule or, more generally, a group of atoms. There are two main types of geometry optimization: determination of the equilibrium geometry at absolute zero ( T = 0 K), corresponding to a fixed atomic position, and the determination of a transition state. In this article, we focus solely on the first type of optimization, which consists in minimizing the energy of the ground state E ₀ at 0 kelvin. The geometric optimization of a molecule or group of molecules consists in minimizing the function...