# Preamble: Part 2¶

Abstract

## Basic assumptions/warnings¶

1. Depends on the BO approximation - isolates the energy purely to be dependent on the geometry of nuclei but not the electrons.
2. A different PES exists for each electronic state of the molecule
3. The PES only corresponds to a single molecule.
4. by its definition it only shows potential energy… not kinetic energy
• Total energy is conserved, so kinetic energy will increase as the potential energy decreases

## Features of the PES¶

You already know this to death..…

• The saddle point shows us the transition state structure not the transition state of the system

## Transition Rate Constant¶

Equation for rate constant of transition structure, according to transition theory, where:

• $$k =$$ Rate constant
• $$k_b =$$ Boltzmann constant
• $T =$ Temperature (K)
• $$\Delta E =$$ $$\Delta G$$ (transition state - ground state) - $$\Delta E$$ refers to a single molecule
• $$R =$$ Gas constant
$k=\bigg(\frac{k_b T}{h}\bigg)e^{\frac{-\Delta E ^\ddagger}{RT}}$

Note

The whole PES is not necessary for these thermochemical calculations..… How can we calculate only the stationary points?